Novak Djokovic continued his 100% record at the China Open Wednesday as he overcame late resistance from Vasek Pospisil, while Maria Sharapova also won but Caroline Wozniacki crashed out.
The number one seed in Beijing was playing at his dominating best in the first set, breaking serve in the third and final games as he appeared in control.
But the Serb lost his trademark composure midway through the second set, screaming to himself in anger as he failed to capitalise on a break point in the fourth game.
Canadian Pospisil was in the ascendency three games later, drawing level at 40-40 with a brilliant cross-court shot which left the world number one flat-footed.
The 41st ranked player in the world then went on to force break-point and took the game following an incredible 26-shot rally.
But his valiant fightback was in vain when a clearly relieved Djokovic won the next game, punching the air with delight and screaming as he made it 5-5.
Djokovic then took the next two games as he closed in on victory, and moments later was dancing to the applause of the crowd as a dejected Pospisil made his way to the court exit.
Pospisil served "extremely well" in the second set, Djokovic said, which put added pressure on his game.
"That's why the second set was very close," Djokovic added following his 6-3, 7-5 victory.
"He had a set point on his serve. But, you know, I fight my way through. I believed I could recover from break down, and I did.
"I think it was, especially in the second set, a very high-quality tennis match."
Djokovic is bidding for his fifth title in Beijing, a tournament he has won every year since 2009 apart from 2011 when he did not take part.
In the women's competition, fourth seed Sharapova got off to a flying start in her match, racing to a 5-0 lead over Carla Suarez Navarro.
The Spaniard was a match for the world number four in the second set, but Sharapova was dominant at the tie-break, finishing the match 6-1, 7-6 (7/3).
World number three Kvitova opened her campaign to win a second consecutive event in China in commanding style.
The Czech player defeated home-crowd favourite Peng Shuai 6-4, 6-2 in her first match since her victory at the Wuhan Open last Saturday, advancing in Beijing with the same confidence she showed at the earlier tournament.
Peng, who made the semi-finals at the US Open last month, took a 2-0 lead before the Wimbledon champion stormed back, winning 12 of the next 16 games and wrapping up the match in just 66 minutes.
Peng throughout the match had difficulty dealing with her left-handed opponent's powerful serves.
"Some of the players, they didn't really get used to left-handers' serves," Kvitova said.
"So I think that's my advantage," she said, adding that "the serve helped me a lot".
Kvitova will now meet 16th seed Venus Williams for a tricky third-round match.
The third seed in Beijing has enjoyed a return to consistency in China after a poor run in the North American swing.
She won her second tournament of the year at New Haven, but crashed out of the US Open in the third round to 145th-ranked Serbian qualifier Aleksandra Krunic.
Kvitova then lost to Elina Svitolina of Ukraine, her quarter-final opponent in Wuhan, in her opening match in Cincinnati.
With her victory in Wuhan, the 24-year-old confirmed her place at the WTA Finals in Singapore, the end-of-season finale involving the world's top eight women players. Those who have already made it to the tournament include world number one Serena Williams, Maria Sharapova (4) and Simona Halep (2).
World number eight Caroline Wozniacki was hoping to confirm her place at the tournament with a deep run in Beijing, but crashed out in her first match at the hands of Samantha Stosur.
Stosur, the 2011 US Open winner, has had a miserable run in China lately, falling at the Guangzhou Open and in Wuhan in her opening matches.
But the world number 21 was the more composed as the two players battled in a tense second-set tie break, saving five set points against her Danish opponent as she wrapped up her 6-4, 7-6 (11/9) victory.
Alize Cornet of France eased past American Lauren Davis 6-2, 6-1 in the day's only other women's match in Beijing, where much of the programme was affected by rain.
The China Open will reach its climax on October 5.