#6 Roman Reigns vs. Brock Lesnar vs. Seth Rollins: WrestleMania 31

At WrestleMania 31, Brock Lesnar defended his WWE World Championship against Roman Reigns. The buildup to their main event clash wasn't the most exciting one, according to many fans. The Royal Rumble winner, Roman Reigns, was certainly not a fan-favorite while going into the match.
People weren't thrilled with The Big Dog main eventing WrestleMania 31 with Lesnar. They wanted The Beast to squash him in less than five minutes. They also didn't expect Reigns to fight back with fervor. As a result, Reigns gave Lesnar a run for his money.
The use of blood during their hard-hitting contest made it look even more realistic. Brock's selling was also on point during the bout, which made Roman seem like an absolute star. However, in the final moments of the match, Seth Rollins pulled off the 'Heist of the Century' by cashing in his MITB contract. He pinned his former Shield Teammate and became the new WWE Champion.
This was technically Brock Lesnar's third defeat at the Grandest Stage of Them All. The biggest thing about this historic cash-in was that Brock Lesnar lost his Championship without even getting pinned by Seth Rollins.
Winner: Seth Rollins
#5 Dean Ambrose vs. Brock Lesnar: WrestleMania 32

Dean Ambrose vs. Brock Lesnar was one of the most anticipated matches of WrestleMania 32. The buildup to this contest was excellent. WWE presented a rivalry that was very different from its usual storylines. Throughout the feud, Ambrose showed his fighting spirit and kept coming back after every beatdown.
He also teased the use of various weapons on the Road to WrestleMania 32. Their match was billed as a No Holds Barred Street Fight. Unfortunately, the PG nature of WWE's modern product didn't allow Lesnar and Ambrose to capitalize on their hardcore strengths. That's why the match ended up being a disappointing affair.
Lesnar completely destroyed Ambrose in this match. Although The Lunatic Fringe did retaliate with some steel chairs, he wasn't able to overcome The Beast Incarnate. Brock ended the match by hitting Dean with an F5 on a bunch of Steel Chairs and walked off the WrestleMania ramp with an easy win.
Winner: Brock Lesnar