Juan Martin del Potro overcame a first set back problem to make a winning start at the Swiss Indoors on Wednesday with a 6-4, 6-1 defeat of Alejandro Falla.
The South American battle between the Argentine second seed and his Colombian opponent ranked 54th finished in just under 90 minutes with del Potro running away with the second set to insure a second-round spot.
Top seed Roger Federer was playing later for the quarter-finals at the home event he has won on five of the last six occasions, facing Brazilian Thomaz Bellucci, whom he beat last March in Indian Wells.
There was trouble for two other seeds at the St Jakobshalle arena, with Frenchman Benoit Paire upsetting last week's Moscow titleholder Andreas Seppi, the number five seed, 4-6, 6-2, 6-3.
Australian Marinko Matosevic put out Florian Mayer, the German seventh seed, 6-2, 6-3. Paul-Henri Mathieu of France beat Swiss-Finn Henri Laaksonen 6-2, 7-5.
Del Potro is hunting for one of two remaining spots in the eight-man year-end championships in London from November 5, standing provisional seventh ahead of French back injury victim Jo-Wilfried Tsonga and number nine Serb Janko Tipsarevic, who quit this week - as did Tsonga - with a physical problem at the Valencia event.
The Argentine broke five times in his victory, his 58th of the season against 14 losses.
Del Potro broke to start the match but was overhauled for 2-all in a game in which he saved three break points.
He took on-court treatment and conferred with a doctor and trainer after the fifth game but carried on with apparent problems to save the opener after three-quarters of an hour after a break in the penultimate game and a love game to finish the set.