World number one Roger Federer was stretched to three sets by unseeded Argentine Mariano Zabaleta in the third round of the Nasdaq-100 Open on Monday.
The top seed survived to win 6-2 5-7 6-3 and set up a fourth-round clash with Croatia's Mario Ancic, who beat 16th seed Tommy Haas.
Ninth seed Andre Agassi also progressed past France's Arnaud Clement.
And fellow American Taylor Dent was in inspired form to beat fourth seed Guillermo Coria 6-3 6-4.
Argentine Gaston Gaudio, the seventh seed, beat Sebastien Grosjean of France 6-2 6-3.
And Florian Meyer of Germany defeated 15th seed Fernando Gonzalez of Chile 7-6 (7-3) 2-6 6-3.
The departure of Coria, last year's runner-up, left just one of the six highest-ranked players - Federer - in the tournament.
Dent has also beaten Lleyton Hewitt, Marat Safin and David Nalbandian this year.
"It's always nice to beat the South Americans and Spaniards at their own little game," said Dent.
Coria admitted: "I didn't play my best tennis today and he played very well,
so it was no surprise.
"He was stronger mentally and came up with bigger shots at the right
Federer was just pleased to go through, saying: "To be on top in the end is really satisfying because it was tough out there.
"Once we got into the third set things were getting harder. The wind came into play and he was getting more pumped.
"The rallies went his way not my way and I had the feeling I was forcing some issues."