Jo-Wilfried Tsonga wowed the O2 Arena with a display of stunning power to see off Mardy Fish at the ATP World Tour Finals and keep alive his hopes of reaching the knockout stage.
Tsonga survived a late wobble to edge the first set and then came from a break down to win six straight games in a ruthless second.
The Frenchman wrapped up a 7-6 (7-4) 6-1 victory in one hour 29 minutes and will be full of confidence going into his final Group B match against Rafael Nadal on Thursday.
Nadal meets Roger Federer in Tuesday's eagerly anticipated late match at 2000 GMT, with Federer knowing a win will guarantee him a place in the semi-finals, while Nadal will definitely advance if he succeeds in straight sets.
"Winning here for first time makes me really happy," said Tsonga, whose only other season-end championship appearance came in Shanghai in 2008.
"Today I played really good tennis and maybe I will have the chance to qualify for the semis, so it's really good. I promise you I will play even better in my next match!"
Defeat leaves debutant Fish in a precarious position at the bottom of the group but - depending on other results - he retains a slim chance of progressing if he beats Federer on Thursday.
The American had lost his only previous meeting with Tsonga and he looked second best again as the sixth seed unleashed a jaw-dropping forehand pass to break serve in the opening game.
Fish volleyed his way back into contention at the first time of asking but Tsonga immediately regained the initiative with the help of a poor line call.
At 0-15 Fish retrieved a drop shot that clearly landed wide, but instead of stopping straight away to request a Hawk-Eye challenge he complained to umpire Carlos Bernardes after losing the point.
By that stage it was too late and Tsonga went on to break for 2-1.
Tsonga held his advantage until game 10 when, serving for the set at 5-4, he failed to reach an inch-perfect lob and handed over two break-back points.
Although the first was saved by a 140mph ace, Tsonga drove a backhand long on the second and they were soon into a tie-break, which the 26-year-old controlled from the outset.
Fish continued to argue with Bernardes over the earlier decision, but he channelled his frustration in the right direction with a break to love in game one of the second set.
That would be the end of his success, though, and Tsonga levelled with a majestic volley before moving 3-1 ahead with a wonderful backhand pass.
The right-hander from Le Mans was now in full flow, treating the fans to an exhibition of power and guile as Fish was given a code violation for smashing his racquet.
The 29-year-old from Minnesota cut a forlorn figure when a forehand sailed wide for 5-1, and he dumped a backhand into the net to complete the formalities.
Earlier, second seeds Michael Llodra and Nenad Zimonjic won their Group B doubles match against fifth seeds Rohan Bopanna and Aisam-ul-Haq Qureshi 7-6 (8-6) 6-3.
Both pairs had lost their opening matches of the tournament.