Stanislas Wawrinka lost in the first round of the Swiss Indoors on Tuesday, damaging his chances of playing in his first ATP World Tour Finals.
Second-seeded Tomas Berdych of the Czech Republic also lost, falling 4-6, 7-6 (4), 7-6 (2) to big-serving Ivo Karlovic of Croatia. Karlovic had 23 aces.
Wawrinka, ranked No. 8, struggled with his serve during his 6-4, 6-3 loss to Edouard Roger-Vasselin.
For 29-year-old Roger-Vasselin, it was a first victory against a top-10 player this season and just the second of his career.
Wawrinka, a U.S. Open semifinalist last month, is eighth in the points race to secure a place in the eight-man finals lineup in London next month.
The ninth player after next week's Paris Masters will advance, because Wimbledon champion Andy Murray is out due to back surgery.
While Berdych is sixth and likely to qualify, Wawrinka is under pressure from Frenchmen Jo-Wilfried Tsonga and Richard Gasquet, who begins in Basel on Wednesday against countryman Michael Llodra.
Wawrinka, seeded No. 4, has now lost his opening match at Basel to a lower-ranked opponent in three of his past five visits.
Berdych lost his first-round match at Basel for the fourth straight time, all against opponents ranked below him.
Seventh-seeded Andreas Seppi of Italy also lost 7-6 (3), 6-3, against Daniel Brands of Germany, who beat Roger Federer at the Swiss Open in Gstaad in July.
The third-seeded Federer will play his second round match Wednesday against Denis Istomin of Uzbekistan, who beat Horacio Zeballos of Argentina 7-5, 7-6 (3).
Kei Nishikori, the No. 6 seed from Japan, eased past Swiss wild-card entry Marco Chiudinelli 6-2, 6-4.
Marcos Baghdatis of Cyprus beat German qualifier Benjamin Becker, 7-6 (8), 6-1, and Ivan Dodig of Croatia advanced after winning just two games when Carlos Berlocq of Argentina retired with an injury.