Mardy Fish might leave Key Biscayne as the top-ranked American in men's tennis, a prospect that leaves him unconvinced.
''I wouldn't be the No. 1 American really,'' said Fish, who beat No. 17 seed Richard Gasquet 6-4, 6-3 in the third round of the Sony Ericsson Open on Sunday.
Fish is ranked a career-best 15th, and if he wins two more rounds he'll overtake longtime friend Andy Roddick in the next rankings. Roddick lost his opening match Saturday and is expected to drop from eighth to about 15th, the lowest he has been ranked since 2002.
''I certainly wouldn't feel like the top-ranked American, considering what Andy has accomplished and what I've accomplished,'' Fish said. ''His career has quadrupled mine, at least.''
Roddick is a five-time Grand Slam finalist who won the 2003 U.S. Open and finished that year ranked No. 1. Fish's record in major events is barely above .500, and he has made the top 20 in the year-end rankings only twice.
But at 29, Fish is in the best condition of his career. That showed against Gasquet in the midday sun on an 87-degree afternoon.
''Playing out there today, you can obviously see why you need to be fit to win these matches,'' Fish said.
No. 2-seeded Novak Djokovic extended his winning streak to 22 consecutive matches by beating wild card James Blake 6-2, 6-0. Djokovic has lost three games in two matches and he's 20-0 in 2011, the best record to begin a year since Ivan Lendl started 25-0 in 1986.
''It has been a dream run for me the last couple of months,'' Djokovic said. ''I'm playing the best tennis of my life.''
Also advancing was No. 30-seeded John Isner, who won an all-American matchup against qualifier Alex Bogomolov Jr., 6-2, 7-6 (4). Bogomolov upset Roddick in the second round, giving Isner a less daunting path to the quarterfinals.
''I didn't want to think too much about it,'' Isner said. ''A lot of times when a draw sort of opens up, guys tend to maybe not play as well. So I'm not looking at the draw.''
This Fish knows: His next opponent will be Juan Martin del Potro, who is gaining momentum in his comeback from right wrist surgery last May. The big Argentine earned his first win this year over a top-10 player by beating No. 4 Robin Soderling 6-3, 6-2.
Del Potro, ranked 484th in February, will climb back into the top 45 after the tournament.
''It's a long road to come back to being at the top again,'' the 2009 U.S. Open champion said. ''I'm improving very, very slowly.''
In women's play, No. 2-seeded Kim Clijsters earned her 500th career victory by beating Maria Jose Martinez Sanchez, 6-4, 4-6, 6-3.
Clijsters, who won the tournament in 2005 and 2010, advanced to the fourth round despite 10 double-faults and 39 unforced errors. She next plays No. 19 Ana Ivanovic, who won when Virginie Razzano retired trailing 2-6, 6-2, 3-0.
Reigning French Open champion Francesca Schiavone, seeded fifth, edged Lourdes Dominguez Lino 6-4, 7-6 (2). No. 9 Agnieszka Radwanska beat No. 24 Maria Kirilenko 7-6 (2), 6-3.
Fish lost to Gasquet twice in 2008, including in the first round at Wimbledon.
''He killed me,'' Fish recalled.
But Fish has won their past two meetings - a reflection of his improved conditioning, he said. After undergoing knee surgery in September 2009, he changed his diet and lost more than 30 pounds.
A slimmer Fish went 40-14 in 2010, a career high for victories, and finished the year ranked 16th, another career best. Willing to play longer points now that he's fitter, his shot selection is less risky, so he makes fewer unforced errors.
''I used to have to go for shots that I don't have to do anymore,'' he said.
Instead, it was Gasquet who made the big mistake - a double-fault on break point in the next-to-last game. Fish served out the victory at love to reach the round of 16, which matches his best showing in 10 appearances at Key Biscayne.
Fish has a 2-2 record against del Potro.
''In the fourth round, every player is playing really well,'' del Potro said. ''So it will be a nice match for both of us.''
