Second-seeded Juan Martin del Potro battled past James Blake 6-4, 7-6 (7/3) Wednesday at the ATP Los Angeles hardcourt tournament as third-seeded Marcos Baghdatis was sent packing.
Argentina's Del Potro, on the comeback trail after a wrist injury cut short his 2010 season, booked a quarterfinal clash with Latvia's Ernests Gulbis.
Baghdatis, however, was bundled out by Taiwan's Lu Yen-Hsun, who defeated the Cypriot 6-3, 6-4 to set up a quarterfinal clash with American Ryan Harrison.
Both del Potro and Baghdatis enjoyed first-round byes, as did top-seeded Mardy Fish and fourth-seeded Thomaz Bellucci.
Fish will open his campaign on Thursday against Luxembourg's Gilles Muller while Bellucci faces Colombian Alejandro Falla in a second-round contest.
After pocketing the first set, del Potro gained the edge in the second when he broke Blake in the third game.
However, the American broke back in the next game and they stayed on serve to the tiebreaker.
Del Potro got off to a quick start in the decider, taking a 3-1 lead and giving himself a 6-2 lead with a forehand winner.
He sailed a backhand wide on his first match point, but made no mistake on the next as he sealed the victory after an hour and 42 minutes.
"It was a really tough match tonight for me," del Potro said, but added that he was happy to be back on US hardcourts, where he broke through for a first Grand Slam title at the 2009 US Open.
His wrist injury prevented him from defending that title last year, but after falling out of the top 400 in the world he has worked his way back to 19th.
"I think I am still far from the top 10 players," he said. "I know it's a long road to be there."
Del Potro next faces Gulbis, a 6-2, 6-4 winner over American Daniel Kosakowski.
Lu looked sharp against Baghdatis, needing just one hour and 13 minutes to notch the victory.
"I didn't really expect this," Lu admitted. "He's a great player with a lot of titles, he has beaten a lot of guys.
"I had a little advantage over him. I had one match behind me and he was playing his first match since Wimbledon."
After racing through the first set, Lu broke Baghdatis in the opening game of the second. Baghdatis never made any inroads, failing to force even one break chance.
After Lu gave himself two match points with a forehand down the line, Baghdatis saved one with a forehand passing winner before sailing a backhand long.
Lu, 27 and ranked 76th in the world, has now matched his best performance of the season after reaching the quarter-finals last week in Atlanta.
He next faces 19-year-old American Harrison, who defeated Michael Russell 6-3, 6-4.
Harrison arrived in Los Angeles buoyed by cracking the top 100 in the world rankings, reaching 94 with his run to the semifinals in Atlanta.
"I warmed up with him this morning," Lu said. "He's a really talented player. It will be a tough match for me -- I don't know if many in the crowd will support me."