Andy Roddick survived two match points to claim a 4-6 6-4 7-6 (7-2) victory over unseeded Argentinian Eduardo Schwank at the Legg Mason Classic on Thursday.
Roddick appeared to be in a good position to advance to the quarter-finals, with a 4-1 lead in the third set after splitting the first two.
However, the top seed lost the next four games and faced two match points before battling back to win in two hours 43 minutes.
Roddick saved 13 of 16 break points in what turned into a marathon three-setter.
"I can't remember the last time I won saving match points," Roddick said.
"It was a tough match. He was playing solid from the back, making me work hard.
"I felt he was a little nervous when he started serving and volleying on big points. I just kept being aggressive and putting pressure on him."
The 25-year-old Roddick is the only seeded player remaining in his half of the draw as number three Feliciano Lopez, number six Marat Safin and number seven Marc Gicquel were all upset in the first round.
As the world number 56, Schwank was the highest-ranked player remaining in Roddick's section - where none of the other six players still involved are ranked in the top 80.
Things could get a bit more tricky if Roddick reaches the final, considering Juan Martin del Potro is into the quarters on the opposite side of the draw, but he has enjoyed a great deal of success here in the past and remains the tournament favourite.
Roddick, the defending champion, will next face Serbia's Viktor Troicki, who beat American Bobby Reynolds 6-4 1-6 6-4.
In other second-round action, Somdev Devvarman of India defeated American Robert Kendrick 6-2 6-7 (7-5) 7-5.
Devvarman faces Russia's Igor Kunitsyn, a 2-6 6-2 7-6 (8-6) victor over Italy's Fabio Fognini.
Legg Mason Tennis Classic second round results:
1-Andy Roddick (USA) def. Eduardo Schwank (Argentina) 4-6 6-4 7-6(7-2)
Viktor Troicki (Serbia) def. Bobby Reynolds (USA) 6-4 1-6 6-4
Somdev Devvarman (India) def. Robert Kendrick (USA) 6-2 6-7(5-7) 7-5
Igor Kunitsyn (Russia) vs Fabio Fognini (Italy) 2-6 6-2 7-6 (8-6)