Daniel Fogg put himself in pole position to claim an Olympic place after finishing ahead of rival David Davies in the FINA Olympic Marathon Swim Qualifier in Setubal, Portugal.
With just one place available on Team GB for the 10km Marathon swim at the Olympics, Fogg has done his chances of selection no harm.
The Commonwealth bronze medallist finished in 35th place in one hour 49 minutes and 38 seconds ahead of Davies who was 38th in 1.50.04.
Both Brits were in the main pack for the first of six laps but by the second, the lead group broke away, leaving Fogg and Davies fighting for the top British spot.
Turning to start his final lap, Fogg pulled away from Davies taking a 17-second lead and held on down the stretch.
Fogg said: "That was a tough race. I didn't really get into my race rhythm and it felt hard throughout from start to finish.
"I couldn't respond to the pack when they made a break and I am disappointed with the final result.
"There will be different conditions in London, so if I get selected, I will hopefully get in and race better."