More anxious moments for Nadal

WIMBLEDON, England -- At almost the exact same time at Wimbledon, Rafael Nadal and Roger Federer, the two most dominant players on the planet in recent years, were in a spot of bother.

Nadal was deadlocked 6-6 with bulldozer Juan Martin del Potro in a tense first-set tiebreaker, while Federer had just dropped the first set to Mikhail Youzhny.

Order was gradually restored. Both would prevail in the fourth round Monday, although Nadal, a 7-6 (6), 3-6, 7-6 (4), 6-4 winner, is the one with more to worry about at the business end of the fortnight. In fact, he has plenty to worry about.

Paradoxically, Nadal, the tour's ironman who sports the kind of muscles that make admirers whistle each time he changes shirts, remains susceptible.

Nadal needed the attention of the trainer against del Potro for a foot injury and thought he'd have to retire.

"I felt terrible," Nadal told reporters.

Already feeling heavy in his legs and on anti-inflammatory drugs, the world No. 1 had almost the same look on his face as at the Australian Open, when a hamstring strain ended his bid to complete the Rafa Slam.

The moment Nadal fans dreaded came immediately prior to the tiebreaker, when he marched up to his chair and planted himself, seconds earlier having damaged his left foot in the midst of hitting a wonderful forehand down the line at 6-5. Nadal said he tweaked the foot earlier in the set.

The timing of the pause was certainly a breach of tennis etiquette and annoyed the imposing Argentine.

A lengthy exchange with ATP trainer Paul Ness ensued, and the tournament doctor also surfaced.

It's "right on the bone" in a "really unusual spot," Ness said in a conversation picked up by microphones. Nadal's facial expressions combined anxiousness and annoyance. Here was another ailment to deal with.

The medical timeout ended with Nadal already having tape on his foot readjusted. Play resumed about 10 minutes later, irking del Potro further.

When Nadal trailed 3-0 in the tiebreaker, the immediate future appeared bleak. As he's done so many times in the past, the defending champion recovered, winning the next four points and eventually sealing the opener on a wild, long del Potro double fault.

"The pain stayed with me for the next points, for sure, and for all the match it stayed with me," Nadal added, aiming to get an MRI "as fast as possible." "But with the tape, I think we changed a little bit the direction of the support and probably didn't hurt me much."

Nadal left for a bathroom break, and del Potro, who would later take an injury timeout himself for an apparent hip problem -- the same hip that rendered him a doubt for the French Open -- voiced his displeasure with chair umpire Carlos Ramos.

Call it a minor miracle that Ramos emerged unscathed. Midway through the first set, he drew the ire of Nadal for, justifiably, issuing a time violation warning. Nadal felt it was unwarranted.

"I think is always the same umpire to do this," he said.

Billed as worthy of a Grand Slam final, the actual tennis dazzled. They went side to side, trading groundstrokes, with del Potro showing more net initiative. He served and volleyed, unlike Nadal, more than a dozen times, counting on floated returns. His slice and volley have developed, and on this form, he's a future Wimbledon champion, adding to his U.S. Open crown.

Nadal can only hope for a recovery similar to last year at Wimbledon, when knee troubles surfaced in the first week before subsiding. His next opponent, Mardy Fish, won't be as keen.

Federer, much less injury prone, has owned Youzhny for a while, entering their duel with a perfect 10-0 record.

As such, the 16-time Grand Slam champion, trying to claim a record-tying seventh Wimbledon crown, didn't panic when losing the first set. He bore down and eventually eased past the Russian, who was slumping prior to Wimbledon, 6-7 (5), 6-3, 6-3, 6-3.

"I thought overall we played a good match from start to finish," Federer told reporters. "Good rallies, good atmosphere. It was fun."

As gifted as Youzhny is, his desire to play flashy shots and get the crowd involved might detract from his focus.

In any case, Federer was the one who produced the shot of the day, uncorking another 'tweener. Not as hard hit as ones in the past, it nonetheless won him the point as Youzhny erred on a smash.

In comparison to his great rival, Federer had the better day. But on a day of major upsets on the women's side, both players can take some solace in the fact that they took the next steps in their quests for the Wimbledon title.

London-based Ravi Ubha covers soccer and tennis for ESPN.com. You can follow him on Twitter.