Top seed James Blake and two-time winner Andy Roddick were both put to stern tests before earning victories and places in the RCA Championships quarter-finals on Thursday.
Blake, who had never been past the first round at the event in three previous appearances, ended the run of Wesley Whitehouse, defeating the South African qualifier 6-7, 6-3, 6-4.
Second seed Roddick laboured to a 7-6, 7-5 third-round victory over hard-hitting fellow American Jeff Morrison.
"I felt I played well all night," Roddick told reporters. "But on every window of opportunity I had, he came up with a huge serve or a great volley.
"I played some of my best stuff this year, but I barely got the win. I was fortunate."
The 2003 and 2004 champion was out-aced 12 to nine by Morrison, who played well above his 183rd ranking.
World number six Blake was broken after a double-fault while serving for victory at 5-2 in the final set, but the American steadied to finally lift the win on the back of 19 aces and four breaks of serve.
"I had to weather the storm," Blake told reporters. "I had a hiccup at 5-2. I may have eased off the throttle a bit.
"When you're serving for the match, things are a little different in your head. I just didn't execute as well as I liked."
The loss ended a career-best run for 512th-ranked qualifier Whitehouse, who upset Marat Safin a day earlier.
Titleholder Robby Ginepri missed a second-set match point but stepped up the pressure to finally defeat Russian Igor Kunitsyn 6-2, 6-7, 6-1.
The 17th-ranked Ginepri now stands a modest 8-16 this season a year after winning his second career title at Indianapolis.
Third-seeded Fernando Gonzalez of Chile overcame American number 14 Vince Spadea 6-4 7-6. Belgian ninth seed Xavier Malisse out-duelled Russian Dmitry Tursunov, the number seven, 7-6, 3-6, 6-3.
Eighth-seeded 2003 finalist Paradorn Srichaphan got out of a 2-4 deficit in his third set against Paul Goldstein, overcoming the American 5-7, 6-3, 7-6 as he saved three match points.
"I thought the match was lost," Srichaphan told reporters. "But he seemed to tighten up as he served for 5-2. We both played well on returns."
The Thai, who has suffered a dozen first-round defeats this season, faces Ginepri on Friday.