The tall, gangly Cristiano Piccini is one of Valencia's unlikely heroes. The Italian right-back popped up in the box in the dying seconds of Valencia's last game of 2018 for a crucial cameo. Valencia were hosting Huesca at the Mestalla Stadium. Valencia's season was in disarray—they were lying 14th in the table, four points from the drop zone.

Things were about to get worse. Only the crossbar saved Valencia from going 2-1 down to bottom-placed Huesca following a late free kick by Huesca's David Ferreiro. With the ref about to blow full-time, Piccini stormed into the box in the last play of the game—with 94 minutes on the clock—and crashed home a left-footed shot first-time into the net. The stadium erupted. It's the only goal he's scored for the club.

"When Piccini scored the winner in the last second for Valencia, the Mestalla celebrated like 'locos,'" says Toni Calero, a journalist with Las Provincias, a Valencia-based newspaper. "It was difficult to understand because in the end to win a match at home against a really inferior team was nothing big, you would think, but it was a turning point in the season.

"The coach, Marcelino, was on the ropes. His team had played a lot of games where they created chances, but they hadn't won. So on a day when a goal goes in in the last second felt brilliant because it changed the dynamic of the team. It helped erase the pain of so many draws, which should have been wins. Valencia have had a lot of heart this season, and that was one of the games that proved it."

Valencia have endured a topsy-turvy season. They couldn't buy a goal in the first half of the season, registering only 17 goals by the halfway stage in their league campaign (the joint-lowest rate in the division). That left them 10 points adrift of the UEFA Champions League places—a mid-season margin that no club had ever made up, according to the statistician MisterChip.

The club miscalculated when it brought in the striker Michy Batshuayi on loan from Chelsea during the summer. Batshuayi had done well on a loan period with Borussia Dortmund last season, scoring seven goals in nine starts in the Bundesliga, and also scoring in the FIFA World Cup with Belgium, but the goals dried up for him in Spain. He only managed one goal in 15 league games for Valencia.

"The move to bring in Batshuayi was negative," says Cayetano Ros, a journalist with El Mercantil Valenciano. "He couldn't score. The players in the dressing room knew the high salary he was earning, and he was playing out of shape, carrying weight. Other forwards were uncomfortable with him—they played less. When he left in January, it opened the door for others to play more and score more. Where the team had been getting draws—16 in 38 league games—they now started to win more. All these draws had been the problem."

Marcelino—who had hauled Valencia back into the Champions League during his first season in charge, following two diabolical 12th-placed seasons—found his head on the block mid-season. He held his nerve. Crucially, he had the backing of his dressing room.

"In Singapore, where the club's owner, Peter Lim, resides, they toyed with dismissing Marcelino," says Calero. "They doubted whether he had the power to drive the team on. Mateu Alemany, the club's general director, convinced Lim to have patience with Marcelino, though, because he saw the work day-to-day that Marcelino was doing and how the players react to him.

"Marcelino understands really well the importance of connecting with his footballers. When you speak to Valencia's players, they all say the same thing: He's very honest—for good and bad. If he has to say something to you, he'll say it to your face, and very clearly, whether a player is in his plans or not. He's a great motivator.

"Marcelino was a professional footballer himself for a long time. He played underage for Spain teams. He understands how a dressing room functions. The team's most important players—Dani Parejo, Rodrigo, [Jose] Gaya—always publicly back Marcelino. One of the abiding images of this season was after Valencia's game against Getafe in the cup when Parejo, the team's captain, embraced Marcelino on the pitch. The pair were practically crying, happy that finally the work they had put in was paying dividends."

When Marcelino was installed in the job in the summer of 2017, he cleared out the troublemakers in the dressing room—including Enzo Perez, Diego Alves and Alvaro Negredo—and persuaded Parejo, who had potential moves to Sevilla and Barcelona on the table, to stay with him. Marcelino has built his team around Parejo, supported by a fine cast of young players, including Goncalo Guedes as well as academy graduates from within—Gaya, who has been capped by Spain, and Carlos Soler.

"The key to Marcelino is that he's a very good psychologist," says Salva Folgado, a journalist with El Pais. "He can cajole his footballers. He likes a dressing room with footballers who aren't in conflict unlike the dressing rooms of a lot of other clubs. He won't tolerate a player in his squad who will be a nuisance or who will generate a bad atmosphere. He's the boss.

"He convinced Parejo—who was on the verge of leaving—to stay. Parejo has said that Marcelino is the best trainer he's worked with during his career along with Ernesto Valverde. Valencia has given Marcelino complete power. He functions like a manager in England, deciding transfers—who comes and who goes—as well as coaching the first team."

Parejo's career has travelled a long and twisting road. He was earmarked for greatness at Real Madrid's youth academy—so highly regarded that club legend Alfredo Di Stefano famously boycotted Real Madrid's reserve team games because he was upset that Parejo had been farmed out on loan to QPR in England.

Parejo's promise went unfulfilled, and he was cut adrift by Real Madrid. He spent a couple of seasons at Getafe before rocking up at Valencia in 2011, where it hasn't always been plain sailing. During Gary Neville's shambolic, four-month reign as Valencia coach during the 2015-16 season, Parejo was stripped of the captaincy, and he got into trouble in December 2016 when he was filmed dancing with a hookah in his hand in a nightclub.

Marcelino has revived his career, however. Last year, Parejo got called up to the Spain national team squad to belatedly win his first international cap at the age of 28. This season no other central midfielder scored as many goals (nine) as Parejo in La Liga.

"Parejo is Valencia's most important player," says Ros. "He directs and organises the team's play. He makes interceptions. Having him in the team relaxes those around him. He's the team's leader, the player with most quality, the most authority and respect. He's one of the best players in La Liga."

Folgado identifies Valencia's Brazilian goalkeeper, Neto, as another cornerstone of Valencia's team. Having spent a couple of seasons as back-up to Gigi Buffon at Juventus, Neto has been a revelation at Valencia since joining at the start of Marcelino's reign in 2017.

"I'm not exaggerating when I say that in 90 per cent of the games that Valencia has played this season, Neto has made a stupendous save that has stopped a definite goal, a save that's helped the team earn points," says Folgado.

"Arsenal are interested in signing him for next season. According to information from a close confidant of Neto's, Neto is still not convinced about the move, but Valencia would have to sell him for the fee they would receive. His buyout clause is €80 million, but he would be sold for about €25 or €30 million."

Neto will have his work cut out trying to keep Leo Messi—who is on course to win his sixth Golden Shoe award as Europe's top scorer—from scoring in Saturday night's Copa del Rey final. Any team with Messi in its ranks is "favourite", says Ros, who otherwise believes the teams are "evenly matched."

Barcelona will start with a depleted side, as they will be missing several star players, including Luis Suarez, goalkeeper Marc Marc-Andre ter Stegen, probably Ousmane Dembele and possibly Philippe Coutinho. After the embarrassing exit to Liverpool in the semi-final of the UEFA Champions League, another humiliating defeat would jeopardise Valverde's position as head coach.

Valencia—who completed a remarkable late-season surge by securing Champions League qualification on the final day of league fixtures—will travel to Sevilla with a more carefree attitude and keen to sign off on the club's centenary year by winning a first trophy since their last Copa del Rey triumph in 2008.

"Valencia's chances depend on the form of Messi. If Messi catches fire, it'll be a big problem for Valencia," says Calero. "Valencia is a very defensive team. It knows very well how to play on the counter-attack. Valencia have a style that Barcelona finds difficult to break down. They've played Barcelona twice this season, and both games ended in draws. This gives Valencia hope.

"Barcelona's elimination from the Champions League against Liverpool did a lot of damage mentally. Valencia's spirits are better. They'll be more relaxed. It's a factor in Valencia's favour."

Follow Richard on Twitter: @Richard_Fitz