Paris - Former Paris Masters champion Tomas Berdych kept alive his hopes of reaching the end-of-season Tour finals with a gritty 6-3, 3-6, 7-5 victory over Portugal's Joao Sousa on Tuesday.
Berdych, who must reach the semi-finals to remain in contention to qualify for London for a seventh straight year, will face 10th seed Roberto Bautista Agut or Gilles Simon in the last 16.
Andy Murray is a potential quarter-final opponent for the 2005 winner, but the Czech appeared unfazed at the prospect of also needing to beat the world number two.
"I have to play good tennis because if you don't play your best, you don't really deserve to be there," said Berdych, who missed the US Open with appendicitis.
"Luckily, I'm healthy and can play. Who would have said that I'd be answering questions about London when I was in the hospital in Cincinnati? This is a nice bonus."
Fourth seed Milos Raonic is one of six players guaranteed their place in the eight-man field in the British capital, and the Canadian brushed aside Pablo Carreno Busta 7-6 (7/5), 6-4.
Raonic, a 2014 finalist in Paris, sent down 17 aces to take his place in the third round where the winner of 16th seed Pablo Cuevas and Paolo Lorenzi awaits him.
Richard Gasquet saved seven set points in the second set to see off Steve Johnson 6-4, 7-6 (13/11), although the 12th-seeded Frenchman is not among the seven players fighting for the two remaining London berths.
American duo Jack Sock and John Isner moved into round two following their respective straight-sets wins over Philipp Kohlschreiber and Mischa Zverev.
Veteran Croat Ivo Karlovic overcame Serbia's Dusan Lajovic in a pair of tie-breaks in his opening match, while Feliciano Lopez defeated French qualifier Pierre-Hugues Herbert.
Novak Djokovic begins the defence of his title on Wednesday against Gilles Muller of Luxembourg, a 6-3, 6-3 first-round winner over Nicolas Almagro.
The record four-time champion has lifted the trophy each of the last three years in the French capital, but his 122-week reign at the top of the world rankings is under serious threat from the in-form Murray.
"I'm hoping that I can finish the season as well as I was doing that in the last couple of years," said Djokovic, who completed a career Grand Slam at Roland Garros in June.
"I had great records in the indoor season and always enjoyed playing in Paris and London.
"So we are coming to the finish line, and as I said, I really do feel comfortable playing in the indoor events and in this surface. So I'm going to take the best out of myself."
Djokovic needs to make the final in Paris to ensure he remains at the top. Failure to do so would see Murray supplant him should the Briton claim a maiden Paris Masters crown.
Murray starts his campaign on Wednesday against Spain's Fernando Verdasco, with the bulk of the seeded players in action after receiving opening-round byes.
Results from the second day of the ATP Paris Masters on Tuesday (x denotes seeding):
Tomas Berdych (CZE x7) bt Joao Sousa (POR) 6-3, 3-6, 7-5
Milos Raonic (CAN x4) bt Pablo Carreno Busta (ESP) 7-6 (7/5), 6-4
Richard Gasquet (FRA x12) bt Steve Johnson (USA) 6-4, 7-6 (13/11)
Grigor Dimitrov (BUL x14) bt Marcos Baghdatis (CYP) 6-3, retired
John Isner (USA) bt Mischa Zverev (GER) 7-6 (10/8), 6-4
Nicolas Mahut (FRA) bt Martin Klizan (SVK) 4-6, 6-4, 6-3
Viktor Troicki (SRB) bt Adrian Mannarino (FRA) 6-4, 3-6, 7-6 (7/5)
Jack Sock (USA) bt Philipp Kohlschreiber (GER) 6-2, 7-6 (7/3)
Feliciano Lopez (ESP) bt Pierre-Hugues Herbert (FRA) 7-6 (7/3), 6-4
Ivo Karlovic (CRO) bt Dusan Lajovic (SRB) 7-6 (7/4), 7-6 (7/5)
Gilles Muller (LUX) bt Nicolas Almagro (ESP) 6-3, 6-3