LONDON (Reuters) - Roger Federer's class shone like a beacon over the murky waters of round-robin tennis with a 6-3 6-2 defeat of Kei Nishikori at the ATP World Tour Finals on Sunday before Andy Murray stayed afloat by defeating Milos Raonic.
The 33-year-old Swiss maestro, bidding for a seventh title at the ATP's year-ending shootout, oozed confidence as he racked up his second consecutive victory in Group B.
However, Murray's 6-3 7-5 defeat of big-serving Raonic means that all scenarios are still possible going into Thursday's matches when group leader Federer faces Murray and winless Raonic takes on Asian trailblazer Nishikori.
Home favourite Murray, beaten by Nishikori on Sunday, had the added pressure of knowing that defeat to Raonic would have eliminated him but the world number six delighted a capacity crowd in the O2 Arena with a steadfast display.
Should Federer win a set against Murray on Thursday he will definitely progress to the semi-finals while Murray needs a straight sets victory to be all but guaranteed a last-four slot.
Nishikori, Asia's first qualifier for the prestige event, would also be well-placed if he beats Raonic with ease, while Canadian Raonic needs a straight sets win to stand any chance of reaching the semis.
Rather than needing calculators and algebra, Federer prefers to let his racket do the math and he was precise again on Tuesday as he outclassed U.S. Open runner-up Nishikori.
After six round-robin matches here in London there is yet to be a three-setter, but Federer's 69-minute masterclass against Nishikori kept the capacity crowd enthralled.
The 17-times grand slam champion needed an ace to fend off an early break point but once he broke Nishikori's serve in the fourth game he was in complete control.
Nishikori, so impressive against Murray on Sunday, showed some flashes of brilliance but was pressured into mistakes by Federer who racked up his 70th win of a stellar season that could yet see him return to world number one.
"I'm happy, you know, after two matches I'm standing here with two wins. It's very positive. That's about it," the imperious Federer told reporters.
While a set against Murray would be enough to take the Swiss through to the semis for the 12th time in 13 appearances at the elite tournament, he will not be taking it easy.
"If it's all to play for, a bit more nerves maybe," he said, before Murray's victory which deprived him of a guaranteed semi-final berth. "At the end of the day, it's how we play every match on tour 'cause if you lose, you're out, so..."
There was nothing spectacular about Murray's performance against Raonic, although the Scot was relieved to get the better of a man who had beaten him three times out of four.
Raonic's erratic forehand buckled in the sixth game of the opening set, gifting Murray a break which proved decisive.
Murray broke early in the second set but Raonic converted a rare opportunity to hit back and looked capable of setting up a deciding set until he wavered at 5-5.
Murray, who played six consecutive weeks to ensure his place in the draw, claimed victory and will now look forward to a make-or-break clash with Federer.
"It's always a pleasure to play against Roger. He's one of the greatest players that's ever played so to get the opportunity to play him in an atmosphere like this is excellent," Murray said.
"On Sunday, there wasn't much magic. But today I came up with some good shots in the right moments. Milos didn't serve as well as he can and that helped."
In doubles play Ivan Dodig (Croatia) and Marcelo Melo (Brazil) maintained their 100 percent record while French duo Julien Benneteau and Edouard Roger-Vasselin also won.
Editing by Ed Osmond and Toby Davis