Dempsey, who came into the final table second in chips, takes home $821,612 plus a $25k seat in the WPT Championship in May for the win.
It wasn't easy, as he had to outlast both a deadly final table and then former November Niner Soi Nguyen over 85 heads-up hands – twice as many as it took to knock out the first four players at the table.
Starting out heads-up virtually even in chips, Dempsey took the lead early before Nugyen battled back to take a 4-1 lead in chips about 40 hands in.
Dempsey stemmed the tide about 20 hands later with a double up before turning things around and taking a 4-1 lead of his own before the final hand.
Sitting with about 12 million in chips, Dempsey min-raised to 300,000 and Nguyen moved in for his last 3.6 million.
Dempsey called with K♥ Q♣ and had Nguyen’s K♣ J♦ dominated.
A J♣ 9♥ 6♣ flop gave Nguyen top pair and the lead but the river T♦ brought the straight and the title home for Dempsey.
Dempsey, known as "Flushy" online, virtually doubles his career live tournament earnings with the win and adds a WPT title to a trophy case that already includes a 2010 WSOP bracelet.
Nguyen earns $517,478 for his runner-up finish.
Back-to-Back Dream Ends Quickly for Esfandiari
Antonio Esfandiari’s vision of back-to-back titles at the WPT Five Diamond Classic didn’t have much time to take shape as he was out in the first ten hands.
Coming in to the final table fifth in chips, Esfandiari tried to make a move early and got it in good with A-T versus Dempsey’s A-4 but a four on the turn put Dempsey at the top of the chip counts and Esfandiari on the rail.
Vitor Coelho was out two hands later in fifth followed shortly by Andrew “LuckyChewy” Lichtenberger, who four-bet all-in with eights only to see Nguyen call with nines.
Vanessa Selbst, a favorite coming in to the final table despite coming in fourth in chips, could only improve one spot and went out in third when her K-9 was dominated by Dempsey’s A-9.
The final six and their payouts, courtesy of wpt.com:
1st: James Dempsey - $821,612
2nd: Soi Nguyen - $517,478
3rd: Vanessa Selbst - $338,351
4th: Andrew Lichtenberger - $218,933
5th: Vitor Coelho - $159,224
6th: Antonio Esfandiari - $119,418
For a full recap of the final-table action, revisit the WPT live updates here.
The next event on the WPT schedule is WPT Venice, set to start Tuesday and run until the 18th. The next WPT event on American soil is the LA Poker Classic at the Commerce Casino Feb. 24-29, 2012.