Feliciano Lopez, ranked 15th in the world, won his Houston debut on Wednesday, beating Paolo Lorenzi 6-4, 7-6 (7/4) to reach the quarter-finals of the ATP Tour US Men's Clay Court Championship.
Lopez, seeded third, belted 13 aces past Italy's Lorenzi to secure the victory in one hour and 56 minutes.
Lopez is seeking to win back-to-back matches for just the second time this year. He reached the round of 16 at the Australian Open, where he lost to Rafael Nadal.
His next opponent is sixth-seeded Argentinian Carlos Berlocq, who became the first player to reach the last eight with a dominant 6-1, 6-0 victory over Germany's Bjorn Phau.
The last three first-round matches were also on Wednesday's slate, with South African fifth seed Kevin Anderson advancing with a 6-3,, 6-4 victory over Brazilian Joao Souza.
Anderson, ranked 33rd in the world and winner of the title at Delray Beach last month, broke Souza five times en route to the victory.
US teenager Ryan Harrison pulled off the upset of the day, downing seventh-seeded Russian Alex Bogomolov jnr 4-6, 6-3, 6-4.
Harrison fired 13 aces and saved nine of the 11 break points he faced.
American Bobby Reynolds withstood a barrage of 19 aces from eighth-seeded Croatian Ivo Karlovic en route to a 7-6 (7/5), 2-6, 6-3 victory.
Karlovic won the Houston title without dropping a set in 2007 and reached the semi-finals last year, but he couldn't find a way past the 116th-ranked Reynolds.
Reynolds earned a second-round clash with defending champion Ryan Sweeting.
The top two seeds in the $442,500 tournament, Americans Mardy Fish and John Isner, were scheduled to open their campaigns on Thursday with second-round matches.
Fish takes on US qualifier Michael Russell.
Isner, who won both of his singles matches to lead the United States to a Davis Cup triumph in France at the weekend, faces Argentinian qualifier Horacio Zeballos.