Going along smoothly and with a three-stroke lead on the final hole of the Irish Open at Adare Manor, the 30-year-old from Hull saw his second shot to the par-five 18th finish on the bank of the River Maigue and, in playing his third, Finch lost his balance and fell into the water.
Although he then three-putted for a bogey six, the former English amateur champion was able to celebrate adding the trophy and a first prize of £330,297 to his New Zealand Open success in December.
Finch, fighting for his future on the European Tour until the final day of last season, shot a closing 70 for a 10-under-par total of 278 and a two-stroke victory over Chilean Felipe Aguilar.
Only 218th in the world entering the event, Finch now stands fifth on the Order of Merit - 105 places higher than he was last season - and is only just outside the top 10 in the Ryder Cup standings.
Welshman Bradley Dredge, keen to make up for losing a play-off to Padraig Harrington a year ago, had been one ahead going into the day, but the curse of the overnight lead struck him. Dredge handed over pole position when he followed an opening three-putt bogey with a double-bogey only two holes later.