St. Preux is a former University of Tennessee football player who shifted his focus to MMA in 2008 and has taken enormous strides in the last year and a half. At the start of 2010 had a 3-4 record and hadn't done anything noteworthy in the cage. But he has really come on of late, improving his record to 11-4 and beating solid opponents including Jason Day, Antwain Britt, Benji Radach and Abongo Humphrey.
None of those opponents is on the same level of Mousasi, who's one of the most talented fighters in the world. Then again, while OSP has been dramatically improving, Mousasi has had an up-and-down couple of years: While fighting in Japan, he's won three easy first-round stoppages over Jake O'Brien, Tatsuya Mizuno and Hiroshi Izumi. But he's struggled in the United States, losing to Muhammed Lawal and fighting Keith Jardine to a draw. In both of those fights, Mousasi showed serious problems stopping takedowns, and until he solves those problems, he's going to have a tough time winning a decision in the United States, where judges frequently favor the fighter who's on top on the ground.
St. Preux is a great athlete who's physically stronger than Mousasi, and it's entirely possible that he could take Mousasi down repeatedly and beat him by decision. The more likely scenario, however, is that the much more sophisticated Mousasi finishes St. Preux.
The Mousasi-St. Preux contest is the first fight Strikeforce has announced for the December 17 card, but other fights expected to take place at that event include Gilbert Melendez defending his lightweight belt against Jorge Masvidal, and Cris Cyborg defending her women's 145-pound belt against an as-yet undetermined opponent.