* Sharapova struggles against British qualifier
* Azarenka flexes muscles in 6-1 6-1 rout of Austrian
* Li shrugs off illness to reach last 16 (Adds Azarenka win, quotes)
TOKYO, Sept 25 (Reuters) - Maria Sharapova pushed the envelope on winning ugly to squeak past British qualifier Heather Watson 6-7 6-3 6-4 and reach the last 16 of the Pan Pacific Open on Tuesday.
The French Open champion's performance bordered on the farcical at times with the second seed carelessly frittering away three set points to surrender the initiative before pulling off an escape act.
By contrast, world number one Victoria Azarenka took 63 minutes, exactly a third of the time Sharapova spent on court, to crush Austrian Tamira Paszek 6-1 6-1 and book her spot in the third round of the $2.16 million Tokyo event.
Li Na, last year's Roland Garros winner, shrugged off a nasty cough to beat Russian Anastasia Pavlyuchenkova 7-5 4-6 6-2.
Sharapova left herself with work to do after a string of double-faults and horror misses gift-wrapped the first set tiebreak to Watson 9-7.
The errors continued to mount but the Russian, her squealing growing increasingly louder with the effort, did just enough to restore parity by winning the second set.
A forehand miss gave Sharapova the break for 4-3 in the decider and the twice Tokyo champion crawled over the line with a big forehand after three hours and nine minutes.
"I definitely felt rusty today," said Sharapova, who served 14 double-faults and finished with 67 unforced errors. "It's one of those matches you're just happy to get through."
One of three Chinese players who made the trip to Tokyo despite a blazing political row between her country and Japan, Li's experience told after a wobble in the second set.
"I'm still not 100 percent," Li told Reuters. "Just trying to stay healthy and taking (cough) medicine every morning and every night."
Azarenka produced an explosive display of hitting to floor Paszek.
"There is definitely a lot of baggage to carry being world number one," said the Belarusian, who won this year's Australian Open and reached the U.S. Open final earlier this month.
"Everyone wants to take your spot. I'm not complaining. It makes it more exciting to know someone is after you. I get more motivated by it."
Li's appearance in Tokyo was a relief for organisers after China withdrew its badminton players from last week's Japan Open amid tensions over disputed islands in the East China Sea.
The 30-year-old saved her best for the crunch points, putting the match away by smashing a cross-court backhand into the corner after two hours and 37 minutes.
Former Wimbledon champion Petra Kvitova was bundled out in the first upset of the WTA premier five event, suffering a 6-4 6-4 defeat by Croatia's Petra Martic.
The fourth seed squandered numerous opportunities against her 72nd-ranked opponent, who closed out the match with a fierce serve which almost knocked the Czech over.
"That was the biggest win of my career so far," smiled Martic. "The last five or six days have been really weird. I've played bad in practice, just couldn't do anything."
Martic next faces Russia's Nadia Petrova after the 17th seed beat Romania's Simona Halep 7-6 6-0.
Nine of the world's top 10 women are appearing in the hardcourt tournament. U.S. Open champion Serena Williams is the only absentee.
Germany's Angelique Kerber made short work of Japanese wildcard Ayumi Morita, the fifth seed comfortably winning 6-3 6-4 to reach the third round.
Sixth seed Sara Errani of Italy beat Sweden's Johanna Larsson 6-3 7-6 and next faces Frenchwoman Marion Bartoli after the ninth seed's 6-2 7-5 win over German Julia Goerges. (Editing by John O'Brien and John Mehaffey)