The Centre Court crowd, buzzing with casual conversation during a changeover, suddenly went silent when the chair umpire uttered words rarely heard at Wimbledon, or anywhere else.
"Ladies and gentlemen," he said, "Mr. Federer is taking an off-the-court medical timeout."
Roger Federer has seldom been slowed by health issues, but he briefly left the court Monday because of a back injury and had spectators wondering whether he would return.
After an eight-minute delay, Federer resumed whacking winners and went on to beat frequent foil Xavier Malisse 7-6 (1), 6-1, 4-6, 6-3. Federer reached his 33rd consecutive Grand Slam quarterfinal, extending his Open era record.
His opponent Wednesday will be Mikhail Youzhny, who beat Denis Istomin 6-3, 5-7, 6-4, 6-7 (5), 7-5.
Federer improved to 10-1 against Malisse. He's 13-0 against Youzhny.
"We know what to expect, both of us," Federer said. "I hope to recover and play a good match against him."
Top seed Novak Djokovic showcased his full armoury of shots as he sauntered into the quarter-finals with a 6-3 6-1 6-3 demolition of countryman Viktor Troicki.
Djokovic came into the encounter on the back of an 11-match winning streak against his opponent and never looked like relinquishing the psychological edge as he broke decisively in the sixth game of the first set before closing it out.
The world number one was in no mood for hanging about in the second, breaking for the third time with a forehand volley to secure the set in just 24 minutes.
Troicki sliced a backhand into the net to hand Djokovic a break in the third and he finished him off to set up a quarter-final against either Richard Gasquet or Florian Mayer, whose match was suspended because of rain.
The constant downpours in south-west London caused two delays, with the second coming just before 5 pm local time before it was announced that there would be no further play.
Among the five men's singles matches to be completed on Tuesday, world number four Andy Murray's clash with Croatia's Marin Cilic, which had been called off with the Scot leading 7-5, 3-1 on Court One.
French fifth seed Jo-Wilfried Tsonga was trailing 6-4, 1-1 against America's Mardy Fish when play was suspended while two other matches - Spain's David Ferrer against Argentina's Juan Martin del Potro and America's Brian Baker against Germany's Philipp Kohlschreiber - were cancelled before play was able to start.
Federer's back began bothering him early in his fourth-round match. He blamed the cool, windy weather and the lingering effects of an arduous five-set win over Julien Benneteau three days earlier.
Federer's serve lacked its usual velocity, but his play seemed otherwise unaffected by the bothersome back. An hour after the victory, he said he already felt much better.
"Honestly I'm not too worried," he said. "I've had bad backs over the years. They go as quick as they came. But of course I have to keep an eye on it now. Two good nights' sleeps, and I'll be 100 per cent on Wednesday. I'm pretty convinced, otherwise I wouldn't have been able to pull out the match the way I did today."
While Federer has undoubtedly felt a back twinge or other discomfort on occasion, he has also played in 51 consecutive Grand Slam tournaments, a testament to his durability. It's unusual to see him require attention from a trainer, but that was the case midway through the first set.
He sat in a changeover chair, leading but ailing, when the trainer came out to check on him. After a brief conversation, they left the court together.
"I felt the back going the beginning of the first set," Federer said. "I asked for the trainer to come out to just talk about it. I decided to have treatment inside."
Federer returned to cheers and gave Malisse a wave of apology for the delay. He then eased any concern about his condition by playing a succession of spectacular points to win the set.
With Malisse serving at 6-5, Federer rocketed a backhand, then sprinted forward to scoop a delicate forehand cross-court for a winner. He hit a backhand winner to reach break point, and put away a deft backhand volley to break for 6-all.
From 1-1 in the ensuing tiebreaker, Federer took the set by sweeping six consecutive points, the last a drop shot for a winner as Malisse slipped behind the baseline and went sprawling.
The Belgian was down but not out. He took the third set and led 2-love in the fourth set before Federer began another surge, sweeping the next five games.
In the final game, Federer hit consecutive service winners, and on match point he whacked an ace at 122 mph, matching his fastest of the day. He shared a warm handshake at the net with Malisse, a friend and foe since both were juniors.
He also has a long relationship with Youzhny, who has been losing to Federer since 2000. The Russian has won three of the 32 sets they've played against each other.
"I never beat this guy," Youzhny said, "so just now I can't talk like about my dreams, what I have to do on court to beat Roger."
Federer and Youzhny are 30, while Malisse is 31. Two other 30-year-olds, Fish and Ferrer, also made the round of 16 — the best such showing by thirtysomethings at a Grand Slam since 1983.
"A good generation," Federer said. "Happy I'm not the only guy left, you know."
Files from AFP were used in this report