Women's bantamweight champion Amanda Nunes (15-4) rides a six-fight winning streak into her third title defense versus challenger Raquel Pennington (9-5) in the main event at UFC 224 this Saturday in Rio de Janeiro, Brazil.

Nunes has not lost in nearly four years, and she is a heavy -700 favorite (wager $700 to win $100) on the UFC 224 betting lines to defeat second-ranked contender Pennington at sportsbooks monitored by OddsShark.

The 29-year-old Brazilian won the title almost two years ago when she submitted Miesha Tate via rear-naked choke at UFC 200, and she followed that up with a stunning first-round knockout of Ronda Rousey at UFC 207 and a split-decision win over Valentina Shevchenko in her last bout at UFC 215.

Nunes may still take on fellow Brazilian Cris Cyborg for the women's featherweight championship, but she said that matchup could have to wait until after she defends her belt successfully here and then again against Ketlen Vieira.

Pennington is listed as a +450 underdog (bet $100 to win $450) and has won her last four fights, with the past three each going to the judges. She sent Tate into retirement following a dominant unanimous-decision victory at UFC 205 in November 2016 but has not entered the Octagon since then.

Pennington's previous two losses both came by split decision against Holly Holm (UFC 184 in 2015) and Jessica Andrade (UFC 171 in 2014). She avenged the latter with a second-round RNC submission at UFC 191.

Two middleweights looking to get the next shot at the 185-pound title belt will also square off in the co-main event when Ronaldo "Jacare" Souza (25-5, 1 no-contest) battles Kelvin Gastelum (14-3, 1 NC).

Souza is a small -150 odds favorite coming off a first-round KO of Derek Brunson that earned him a Performance of the Night bonus at UFC on Fox 27 on January 27. Current champion Robert Whittaker knocked him out in his previous bout at UFC on Fox 24 a year ago with a title shot on the line.

Meanwhile, Gastelum is finally fighting at a more comfortable weight after struggling with cuts at welterweight (170 pounds). He is a +120 underdog and has gone 2-1 with a no-contest since jumping back up to middleweight, knocking out former champ Michael Bisping in his most recent performance at UFC Fight Night 122 in China last November.

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