Stan Wawrinka highlighted his first-set performance against Andy Murray as the decisive moment in the winner-takes-all round-robin contest at the ATP World Tour Finals on Friday.
Swiss fourth seed Wawrinka advanced to the semi-finals of the season-ending tournament for a third successive year after ousting Murray 7-6 (7-4) 6-4 in the concluding group-stage clash in London.
Wawrinka was forced to dig deep in the opening set at the O2 Arena, rallying from 4-2 down in the tie-break and winning five consecutive points to close the first stanza in one hour, seven minutes.
The French champion then went on to serve out the match, despite a late wobble, as he set up a mouth-watering semi-final with countryman Roger Federer.
"The first set was important, as it is always tough to beat Andy," said Wawrinka, who lost a three-set thriller to Federer in the semis last year.
"I'm sorry for the crowd that I had to beat him, but I am happy to be in the semi-finals.
"The next match will be interesting and we played a crazy match last year. It is always difficult to play against him, and I will need to rest a lot before tomorrow.
"It was an amazing atmosphere and hopefully I will see you all tomorrow."
Wawrinka added: "It's an amazing tournament to play. It's a big chance to be in the top eight at the end of the year.
"I always try to enjoy it. I always try to give everything. The conditions are normally quite good for me. But you also play only the top eight guys.
"If you look at the last two years, almost two and a half, I started to beat a lot of the top guys. I started to be really confident against them, that I have the game to beat them."