Venus Williams defeated unseeded Italian Flavia Pennetta 7-6, 6-2 in Sunday's Zurich Open final to all but guarantee the American a place at the season-ending WTA Championships in Doha.
Third seed Williams, who had lost her last three meetings with Pennetta, took full control of their latest encounter after rampaging through the first set tiebreak 7-1.
Sunday's victory will lift Williams comfortably clear of rivals Vera Zvonareva and Agnieszka Radwanska in the race for the last two Doha qualifying spots when the latest standings are published on Monday.
Radwanska, in the worst position of the trio, will now have to win both the remaining tournaments in Linz and Quebec, where she is not currently entered, to deny Williams a place at the finale.
In keeping with her previous poor record against Pennetta, Williams was made to work hard during the opening stages of Sunday's match with neither player offering up a single break point during the first set.
The subsequent tiebreak proved surprisingly one-sided, however, with Williams storming into a 6-0 lead after forcing two early errors from her opponent with a couple of powerful groundstrokes directly to Pennetta's feet.
After losing the tiebreak, Pennetta could find no way back.
Dropping her serve for the first time in the third game of the second set, she then had to watch as Williams fired in four straight aces to lead 3-1.
Following a further break of the Italian's serve, Williams was denied her first chance to wrap up the match when a Pennetta backhand on match point which looked long was controversially ruled in.
Williams kept her cool, hitting a fierce winner to the corner of the court before producing a final service winner.