Tsonga sneaks through in Thailand

Top seed Jo-Wilfried Tsonga opened the defence of his Thailand Open crown with a tricky 6-7 7-6 7-6 win over Latvian Ernests Gulbis to reach the quarter-finals on Thursday.

The Frenchman had to win two tie-breaks to get past the Latvian in a tense two-hour 12-minute match, his first outing in the $608,500 tournament.

Big serves dominated the match, with Tsonga firing 20 aces to Gulbis's 23 in a closely fought encounter that the Latvian was unlucky to lose.

The seventh-ranked Tsonga will meet Switzerland's Marco Chiudinelli in the last eight after he ousted former world number one Marat Safin.

The temperamental Russian continued his miserable run of form ahead of his retirement, going down 6-3 7-6.

Second seed Gilles Simon shrugged off knee trouble to seal a 6-2 6-2 win over American Kevin Kim and book his place in the quarter-finals after almost a month off the circuit.

Simon, who has not played since retiring injured at the U.S. Open early last month, played a solid service game, blasting 11 aces to seal an impressive comeback win.

"I didn't know what to expect but I played a good match," Simon told reporters. "My knee is still shaky but I tried not to think about it. I can play today, but sometimes, it's painful."

Lofty American John Isner booked his place in the last eight with a 7-6 6-4 win over German Mischa Zverev.

The eighth seed was sluggish in the opening exchanges but served well and kept his composure to advance. He will take on fourth-seeded Serb Viktor Troicki in the next phase.

German Andreas Beck also progressed after beating American lucky-loser Donald Young 6-1 6-7 6-4 and faces Austrian sixth seed Juergen Melzer on Friday.