Basel - Roger Federer will take a 5-0 lead into his second-round match at the Swiss Indoors on Wednesday as he faces Denis Istomin for a spot in the quarter-finals of the home event he has won five times.
The Uzbek challenger, ranked 48th, earned his place against Basel-born third-seed Federer through a 7-5, 7-6 (7-3) defeat of Argentine Horacio Zeballos.
Federer last beat Istomin while nursing a bad back in March at Indian Wells.
Federer is in the chase for one of the four remaining spots at the eight-man World Tour Finals in London starting a week from Monday.
After a poor season in which he admitted to mistakes in scheduling and trying to play through injury, the world number six - winner of only one title in 2013 - is on red alert this week at home and next week at the Paris Masters, last tournament of the ATP regular season.
He trails compatriot Stanislas Wawrinka by just 40 ranking points in the race to London, standing provisional eighth to the seventh of US Open semi-finalist Wawrinka, who has never played at the year-ender.
But Wawrinka did himself no favours as he bowed out 6-4, 6-3 in his opening match, ending on a double-fault against Frenchman Edouard Roger-Vasselin.
There was also an early disaster for Tomas Berdych as the second seed and London candidate was beaten by second Ivo Karlovic, who fired 23 aces in a 4-6, 7-6 (7-4), 7-6 (7-2) upset.
Berdych served for a win without success and found himself adrift in a tiebreaker on the way to defeat.
Wawrinka, who beat holder Andy Murray at the US Open, lost in 71 minutes. After dropping the opening set, Wawrinka then began the second the same way and was unable to close the gap.
It was a big match for me, playing in front of the Swiss people and I didn't handle it well," said Wawrinka. "I have to accept it.
"But I'm still having the best season of my career and I can't forget that."
His year-end campaign now rests with the Paris Masters. "I will go to Paris early and practise, I need to be ready."
Japanese sixth seed Kei Nishikori sent local Marco Chiudinelli, a wild card entry and childhood friend of Federer, out 6-2, 6-4 in the first round, Nishikori played the final against Federer in 2011, the last time the home hero won the title.
Chiudinelli, 32, has played Basel nine times and reached the semi-final four years ago to lose to Federer.
Nishikori will bid for the last eight against Ivan Dodig after the Croatian needed just nine minutes on court as Argentine Carlos Berlocq quit injured trailing 2-0.
Marcos Baghdatis lines up against either defending champion Juan Del Potro or Swiss wild card Henri Laaksonen after beating German qualifier Benjamin Becker 7-6 (10-8), 6-1. German Daniel Brands upset Italian seventh seed Andreas Seppi 7-6 (7-3), 6-3.