Boxing icon Claressa Shields is undefeated as a pro boxer with a perfect 13-0 record. She also competed as a mixed martial artist in the PFL and tasted defeat in that sport. But has Shields never suffered a defeat in the boxing ring? If yes, then who defeated her in the sport? Let's explore.ESPN MMA@espnmmaAbigail Montes defeated Claressa Shields by split decision at the 2021 #PFLChampionshipIt was the first loss of Shields' professional fighting career.1823224Abigail Montes defeated Claressa Shields by split decision at the 2021 #PFLChampionshipIt was the first loss of Shields' professional fighting career. https://t.co/PPTLjpe40lWho defeated Claressa Shields?At the 2012 Women's World Championships held in China, Claressa Shields suffered her only amateur loss at the hands of Savannah Marshall. Subsequently, she was eliminated from the tournament and had to wait another two years before claiming gold.Both boxers have since progressed to become world champions, but Shields continued to seek her revenge. After years of constant verbal exchanges, the two met on October 15, 2022, at the O2 Arena in London.Ring Of Highlights@ringofhighlightClaressa Shields comes out throwing everything in RD1 #ShieldsMarshall521132Claressa Shields comes out throwing everything in RD1 😳 #ShieldsMarshall https://t.co/xlklj2r2KPMarshall found success only when she tried to impose her size and strike Shields' body. However, it wasn't enough, as Shields took most of the rounds and won by a clear margin according to all three judges' scorecards.The win awarded Claressa Shields a new belt to add to her ever-growing collection, the WBO female middleweight title, and some sweet revenge.ESPN Ringside@ESPNRingsideHISTORY @Claressashields becomes the only fighter (male or female) to become undisputed champion on 3 different occasions after her win at #ShieldsMarshall1841591HISTORY 🏆@Claressashields becomes the only fighter (male or female) to become undisputed champion on 3 different occasions after her win at #ShieldsMarshall https://t.co/IK8XHLiriCWho defeated Claressa Shields in MMA?Claressa Shields competed in MMA from 2021 to 2024, amassing a professional MMA record of 2-1. The only loss of Shields' professional MMA career came against Abigail Montes at PFL 10 in October 2021.Shields was expected to emerge victorious. However, Montes' grappling skills proved decisive in neutralizing Shields' striking game. After a relatively close two rounds in the lacklustre bout, Montes secured a takedown at a crucial point in Round 3, controlling Shields from the top position. Two of the three judges scored the contest in Montes' favor, declaring her the winner by split decision.Shields returned to MMA competition after more than two years of absence and defeated Kelsey DeSantis by split decision at the PFL vs. Bellator event in February 2024. In May 2025, Shields announced her retirement from MMA competition.