Victoria Azarenka has squeezed past Serena Williams in a tense tie-break decider to win the Cincinatti Open.

Williams looked in confident mood early on and wasted no time in wrapping up the first set, taking advantage of some early Azarenka struggles on serve to claim the opener 6-2.

Both players traded a whole host of break-point chances in a strange second set, which included Williams battling to hold serve in a game featuring 10 deuces.

Eventually Azarenka broke her opponent's resistance to level the match in style, holding from 0-40 down to claim the second set.

Midway through the third and final set Azarenka looked to have edged ahead decisively as she broke to go 4-2 up, but Williams quickly responded in kind with an emphatic break of her own.

As both players stayed calm on serve a third-set tie breaker was required to decide a tight final set, with Azarenka rising to the challenge.

The 24-year-old seized on a pair of untimely mistakes with the breaker deadlocked, as Williams sent a backhand long before double-faulting at 6-6 to hand her opponent match point.

Azarenka made her chance count at the second time of asking, forcing an error as Williams blasted into the net to claim a 2-6 6-2 7-6(8).

The world number two's hard-court record now stands at 29-1 heading into next week's US Open at Flushing Meadows.