Britain's Andy Murray edged out Spain's Fernando Verdasco in the Paris Masters second round as he aims for the world number one ranking.
Murray, 29, who could overtake Novak Djokovic with a good run this week, won 6-3 6-7 (5-7) 7-5 in two hours and 29 minutes despite a patchy display.
Earlier, Djokovic beat Luxembourg's Gilles Muller 6-3 6-4.
The Serb, 29, will retain his number one ranking - held for 122 weeks - if he reaches the final.
However, failure to do so would allow Murray to overtake him if the Scot can win the title, or if Murray reaches the final and Djokovic exits before the semis.
Murray took the first set against Verdasco, after breaking to go 4-2 ahead, but lost a second-set tie-break after both players twice had their serves broken.
|Paris Masters Thursday schedule (Court Central - starting at 10:00 GMT)|
|Marin Cilic (Cro)  v David Goffin (Bel) |
|Richard Gasquet (Fra)  v Jack Sock (US)|
|Novak Djokovic (Srb)  v Grigor Dimitrov (Bul) |
|Lucas Pouille (Fra)  v Andy Murray (GB) |
In a tense decider, Murray struggled to dominate the world number 46 before breaking to love to clinch a place in the third round.
Murray faces Frenchman Lucas Pouille at about 17:00 GMT on Thursday, while Djokovic plays Bulgarian Grigor Dimitrov.
Victory over Verdasco means Murray, who secured his seventh title of the year in Vienna on Sunday, has won 53 of his past 57 matches.
"It wasn't the best match from my side," said Murray. "I got through it.
"It was a tough match. Verdasco was going for his shots and serving huge.
"When he was behind in games and even when I was getting the return back, he was dictating the points on his forehand and backhand. He hit a few lines with his backhand. I just had to fight at the end."
The battle for top spot
Murray, who won his third title in as many weeks with victory in Vienna, is bidding to top the rankings for the first time.
But four-time Paris champion Djokovic looked composed as he returned to action after losing in the Shanghai semi-finals two weeks ago.
The top seed took the first set after breaking in the sixth game, then broke again to go 5-4 up in the second to win in an hour and 20 minutes.
"It was great to start off the way I did today," said 12-time Grand Slam champion Djokovic.
He completed the career Grand Slam with a first French Open title in June, although his form has dipped since then.
Djokovic won in Toronto but lost early at Wimbledon and the Olympics, and was beaten in the US Open final by Stan Wawrinka.
Murray has closed the gap dramatically in terms of points over the past four months to trail by only 415, with 1,000 on offer to the winner in Paris.
Earlier on Wednesday, Japan's Kei Nishikori claimed his 300th career win, a 6-2 7-5 victory against Serb Viktor Troicki.