(Sports)Kei, Serena, Wawrinka stutter at Australian Open

The top seeds continued the trend of comeback wins as Serena Williams, men's defending champion Stan Wawrinka and Asia's top ranked male, Kei Nishikori, showed vulnerability in the second round of the Australian Open on Thursday.

A day after Rafael Nadal, Roger Federer and Maria Sharapova were all forced to fight back from a set down, Kei was far from his best against Croatia's Ivan Dodig, who took the first set and only narrowly missed the second.

The Number one male player, Novak Djokovic, had no problems, however, mercilessly bulldozing Russian Andrey Kuznetsov 6-0, 6-1, 6-4.

Nishikori, who eventually found form to win 4-6, 7-5, 6-2, 7-6 (7-0), said he was not yet playing his best tennis.

"I think I'm getting close," said Nishikori.

"Maybe these couple of matches weren't played at 100 percent but I'm still winning in three or four sets.

"I think it's getting there."

The early problems for the off-key Nishikori were compounded by a clean-striking Dodig, who forced the world Number five to play at every ball.

Nishikori was broken in just his second service game and never recovered in the opening stanza, with his error count hampering efforts to break back.

He found trouble again in the fourth set only to break back as Dodig served for the set and then race through the tiebreak.

"I thought he was playing really well, especially in the first couple of sets," said Nishikori.

"He was really aggressive and returning well.

"I was struggling with my service game especially but, in the third and fourth sets, I started playing more aggressively."

The highest ever ranked player from Asia will next play the United States' Steve Johnson whose 6-3, 6-4, 6-2 win knocked out 30th seed Santiago Giraldo.

Five-time Australian Open champion Serena Williams was forced to save three set points before she took the first set and ran away with the match to progress with a 7-5, 6-2 win over Vera Zvonareva.

Zvonrareva, a former world Number one who lost to Williams in the 2010 Wimbledon final, was on the verge of breaking the world Number one for the second time at 3-5, only to lose the next ten games.

"Things really clicked," said Williams.

"I had no option but for things to click."

Serena's sister, Venus, also won through to Saturday's third round with a straight-sets win over compatriot Lauren Davis.

"She's really motivating," said Serena.

"It makes me look behind my shoulders and I have to play better, I want to do better."

The defending men's champion, world Number four Stan Wawrinka, faced a 242-km serve from Marius Copil and struggled to get a racquet on those marginally slower.

Wawrinka, however, prevailed in each of the match's two tiebreaks before breaking the fast, if sporadic, serve of Copil to win 7-6 (7-4), 7-6 (7-4), 6-3.

"He was playing great. He was serving big and putting lots of pressure on," said the fourth seed.

"I wasn't playing my best tennis but I'm happy with the way I fought today and the way I did win the match."

Frenchman Adrian Mannarino almost pulled off a big upset against Number 12 seed Feliciano Lopez after leading two sets to love and 4-0 in the third.

Mannarino was overcome by heat stress as the temperature pushed beyond 32 degrees and, after looking on the verge of fainting over the final twenty minutes, he retired with the score at 4-6 4-6 7-6 (7-3) 4-0.

American John Isner will play Luxembourg's Gilles Muller after both advanced in long four set matches.

The winner of that will most likely play Djokovic in the fourth round in the second week.

In the women's draw, Alize Cornet gave French hearts a flutter when broken twice in the third set of her match against qualifier Denisa Allertova before the 19th seed won 6-4 6-7 (7-2) 6-2.

Two-time Wimbledon champion Petra Kvitova had no such troubles to breeze past unseeded Mona Barthel 6-2, 6-4.

However, the performance of the day remained with fellow title hope Agnieszka Radwanska who was off court before midday.

The 2014 Australian Open semi-finalist's emphatic 6-0, 6-1 win over Sweden's Johanna Larsson took a mere 44 minutes and means she has only conceded four games for the tournament. Endi