Roger Federer missed the chance to secured qualification for a 12th consecutive appearance at the ATP World Tour Finals in London after Juan Martin del Potro retained his Basel indoor title with a three set win over the 17-time grand slam champion to secure his passage to the season's ending finals.
The Swiss requires a round two win over Kevin Anderson or Mikhail Youzhny at the Paris Master, in the climax to the regular season, to book his place in next week's event in the English capital while fellow-countryman Stanislas Wawrinka is also closing in on qualification.
"I'm a winner type, I don't take that much confidence from losing matches," Federer said of his run in Basel, where he is a five-time former champion.
"I'm happy about the level of play, that it's getting better, but it's not in losses where I find my confidence. It's in wins. I think the four matches previous gave me more than today's match."
Wawrinka faces Spaniard Feliciano Lopez or Australian Bernard Tomic in round two and would all but secure passage to the season ending finals for the first time should he beat Nicolas Almagro in the third round.
Almagro, currently world No.12, is among three players who must win in Paris to stand any chance of finishing in the top nine, with Tommy Haas and Youzhny also needing to lift the title. Milos Raonic needs to at least reach the final but will likely have to beat already qualified trio Tomas Berdych, David Ferrer and Rafael Nadal this week.
The tussle for the final qualification berth is likely to be an all-French affair with Richard Gasquet and Jo-Wilfried Tsonga's likely third round meeting expected to prove pivotal should Wawrinka win his opening match.
Tsonga, a former runner up in London, suffered a second round exit at Wimbledon and missed the US Open with a knee injury to dismantle his 2013 season, while Gasquet has enjoyed a renaissance this year, the highlight being his semi-final appearance at Flushing Meadows.
Novak Djokovic will be opening to eat into Nadal's advantage at the top of the ATP rankings ahead of London but with the Spaniard having no points to defend in Paris the Serb needs a long run before an assault on defending his title at the O2 Arena in order to snatch away the world No.1 ranking.