Taiwan's Lu Yen-Hsun toppled third-seeded Marcos Baghdatis 6-3, 6-4 on Wednesday to reach the quarter-finals of the $619,500 ATP Los Angeles hardcourt tournament.
Lu, who got through a tough first-set match against American Robby Ginepri as Baghdatis enjoyed a first-round bye, looked sharp on Stadium Court, needing just 1hr 13min to oust the Cypriot.
"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 is 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 rising American Ryan Harrison, who defeated Michael Russell 6-3, 6-4.
Harrison, 19, arrived in Los Angeles buoyed by cracking the top 100 in the world rankings, reaching 94 with his run to the semi-finals 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."
In another early match, Latvia's Ernests Gulbis defeated young American Daniel Kosakowski 6-2, 6-4.
Gulbis next faces either second-seeded Juan Martin del Potro of Argentina or US veteran James Blake.
Del Potro, whose ranking fell as low as 484th in the world after a wrist injury cut short his 2010 season, has climbed back to number 19 and is keen to keep improving as the US Open approaches.
Del Potro won the US Open title in 2009 but was denied a chance to defend his first Grand Slam title because of his wrist injury.