Rafael Nadal reached the final of the Swiss Indoor tournament when he beat Frenchman Richard Gasquet 6-4 7-6(7), a result that was good news for fellow Spaniard David Ferrer.
Gasquet could still have denied Ferrer a place in the ATP World Tour Finals next month, but his defeat means Ferrer, along with Japan's Kei Nishikori, complete the eight-man line-up for the season-ending showpiece.
Nadal was a break down in the opening set but hit back from 2-4 to win four consecutive games.
He also trailed 6-4 in the second-set tiebreak before reeling off the last four points.
Standing in the way of Nadal in his 98th career final will be top-seed and home favourite Roger Federer who beat American Jack Sock 6-3 6-4 in little over an hour.
Federer is looking for a seventh title in his home city.
Ferrer and Nishikori join three-time defending champion and 2008 winner Novak Djokovic, Andy Murray, six-times former winner Federer, Stan Wawrinka, Tomas Berdych and Nadal in London.