Novak Djokovic started his bid to regain the world number one spot with a comfortable 7-5 6-1 win over Portuguese qualifier Joao Sousa at the Paris Masters.
The Serbian has won 19 consecutive matches and is aiming to move ahead of Rafael Nadal in the next set of ATP rankings following the French tournament.
Number two seed Djokovic, who had been given a bye in the first round, took time out during the match when play was stopped for a spectator to receive attention after falling ill, handing the man a towel.
Djokovic had opened up a 4-0 lead during the second set before closing out victory in just over an hour and a half.
Damir Dzumhur will be his third-round opponent after the Bosnia and Herzegovina player recorded an unexpected 6-3 6-3 win over Greek number 14 seed Stefanos Tsitsipas.
In Tuesday's late match at Bercy, fifth seeded Croatian Marin Cilic came through 6-3 6-4 against Germany's Philipp Kohlschreiber.
Russian Karen Khachanov also moved into the third round after Matthew Ebden retired during the second set, when the Australian was trailing 6-2 2-0.
Earlier in Tuesday's first-round matches, Spain's Fernando Verdasco secured a clash against top seed Nadal after his 6-4 6-4 win over home player Jeremy Chardy.
Gilles Simon came through the all-French clash against Lucas Pouille, with a 6-3 6-4 victory.
Milos Raonic produced a stirring comeback to end the hopes of wildcard Jo-Wilfried Tsonga in a match which lasted almost three hours.
The Canadian secured his place in the second round against world number three Roger Federer after battling to victory, 6-7 (4) 7-6 (5) 7-6 (5)
Russian Daniil Medvedev also progressed after his 6-2 6-2 win over Pablo Carreno-Busta.
French hopefuls Benoit Paire and Pierre-Hugues Herbert, though, both lost in round one, with Marton Fucsovics of Hungary and Kazakhstan's Mikhail Kukushkin winning their respective matches.