Toronto, Canada – By Ian Ransom
Clijsters, who appeared to be cruising after breaking Tamarine early in the first set, suddenly met stiff resistance from the 99th-ranked Thai veteran in the second.
The Belgian found herself trailing 3-1 after being broken, but struck back and battled to hold on to her serve after winning a couple of marathon games.
"I haven't played her for a few years. I was actually surprised to see she was still playing," Clijsters said of the 32-year-old Tamarine, a surprise quarter-finalist at Wimbledon in 2008.
"But she's very tricky. She doesn't give you anything where you can just step in and hit a lot of winners or really go for a lot.
"So I just had to kind of be patient, wait for the right shot to go for it."
She looked sharp early under a sun-drenched Rod Laver Arena, mixing baseline power with the occasional deft drop shot to break Tamarine and race to a 4-1 lead in the first set.
After sealing it with a rocketed cross-court forehand winner, Clijsters found herself on the back foot, however, when Tamarine began attacking her serve with abandon.
The Thai broke Clijsters to take a 2-0 lead, but handed it back shortly after and was unable to contain the Belgian's push to the finish line.
Clijsters, seeded 15th, will next play Russia's Nadia Petrova, who she has beaten in each of their previous four matches.
"Usually tall girls, they're not the greatest movers around," said Clijsters of the 1.78 meter (5-ft-10) Petrova.
"Obviously that's something that I'm definitely going to try to take advantage of."
(Editing by Alastair Himmer)