This time a year ago, James Blake was so dizzy when he ventured out of his house that he feared he might fall. And when he tried hitting tennis balls again he actually flinched, afraid a ball might smack him in the head because he couldn't see clearly. His smile was nonexistent. There wasn't much to smile about, for one, losing his father to stomach cancer and, by all indications, losing a promising tennis career to a broken neck. Had there been cause for joy, he couldn't express it because one side of his face was paralyzed -- a result of the shingles that also damaged his hearing and rattled his balance.

On Saturday Blake couldn't stop smiling after plopping in his courtside seat at the U.S. National Tennis Center, overwhelmed by what he had just accomplished.

In toppling the world's No. 2 player, Rafael Nadal of Spain, 6-4, 4-6, 6-3, 6-1, Blake advanced to the fourth round of the U.S. Open, equaling his best performance in a Grand Slam event, and proved he's again ready to compete with -- and defeat -- the world's best.

Blake credited his stunning victory to the new perspective he gained after last season's struggles and his freefall in the rankings, from 22nd in the world to 210th. Not a day goes by that he doesn't think about his father, he said, and that fact that he told him he was proud of his son during one of their last conversations.

"He always taught me about work ethic and doing your best and acting appropriately," Blake said. "I feel like I did that today. Whether I won of lost, I gave 100 percent. I acted according to the manner that I know he would think is appropriate. So if I won or lost this match, I'd like to think that he was proud of me."

Though Blake's performance steadily improved this summer (he reached the final of Washington's Legg Mason Classic and won his second career title at New Haven, Conn.), he needed a wild card to qualify for his fifth U.S. Open. But he hardly played like an also-ran against Nadal, swamping the Spaniard with mighty forehands, smartly placed serves and superior strategy.

The match presented a delightful contrast in styles. The right-handed Blake was determined to attack at every opportunity; the left-handed Nadal was content to counterpunch and wait for the slightest hole in Blake's net coverage to blast a passing shot by him.

Blake knocked the muscle-bound Spaniard on his heels with 10 aces, and he blistered the court with 53 winners while committing just 27 unforced errors. In vanquishing Nadal, Blake moved one round closer to a quarterfinal meeting with Andre Agassi, his hero, on Wednesday. Agassi did his part to develop the storyline later in the day, defeating Tomas Berdych of the Czech Republic, 3-6, 6-1, 6-4, 7-6 (7-2).

Also advancing was top-ranked Lindsay Davenport, who romped, 6-3, 6-2, over Anabel Medina Garrigues of Spain. American Robby Ginepri defeated Tommy Haas of Germany, 7-5, 6-7 (7-3), 6-4, 2-6, 6-3, for the right to join Blake and Agassi in the fourth round.

Though a heavy underdog, Blake strode onto the court at Arthur Ashe Stadium with the backing of a raucous, sellout crowd that took its cue in fist-pumping and chanting from 77 of his closest friends and family members, who jammed into suites that ringed the venue's second and third tiers. And afterward his cell phone was so inundated with congratulatory calls that most well-wishers -- including Andy Roddick, who was bounced in the tournament's first round -- had to leave messages.

Clad in his trademark Capri pants, the 19-year-old Nadal opened play with utter abandon, running down Blake's flat groundstrokes with energy to spare. With muscles rippling under his skin-tight shirt and eyes blazing, he looked fit enough to run for days, happy to trade shots from the baseline for as long as it took.

The first set stayed on serve until Blake finally broke the Spaniard in the ninth game. It was only the second time Nadal has lost his serve all week. Then he served out the set by yanking Nadal wide for a service winner.

Nadal seized the momentum in the second set, getting the break with Blake serving at 4-5 when the American netted a forehand. The Spaniard pirouetted in the air and skipped to his seat.

Instead of doubting his tactics, Blake dug in and drove his groundstrokes harder. Fans rewarded him for every risk, cheering "Blake! Blake! Blake!" when he won the point and "Blake! Blake! Blake!" when he lost a point.

Nadal paid dearly for a few sloppy points in the third set. Blake broke him with a perfectly placed lob in the fifth game and broke him again on another lob to close the set, 6-3. After that the confidence seemed to drain from Nadal's body, and Blake rolled through the decisive set in 23 minutes, winning 16 of the last 17 points.

"He has a very good forehand. He's fast. And he plays with confidence," said Nadal, whose nine titles this season (including the French Open) are matched only by world No. 1 Roger Federer.

Blake moves on to a fourth-round match Monday against Sebastien Grosjean or Tommy Robredo. A victory would send him into Wednesday's quarterfinals, where Agassi might be waiting -- a prospect Blake deemed too wonderful to contemplate. "If someone had told me a year ago that I'd have to go out and lose [6-]0, [6-]0, [6-]0 in the quarterfinals of the Open to Andre Agassi," Blake said, "I'd take it in a heartbeat."

James Blake, whose ranking tumbled to 210th last year, enjoys his victory over second-seeded Rafael Nadal.