The reigning Wimbledon, French Open and U.S. Open champion Nadal has now won his last 17 matches at the All England Club, where he titled in 2008 and again last year. The Mallorcan strongman, who missed the 2009 edition because of injury, hasn't lost here since giving way to Federer in the 2007 final.
The 10-time major champion Nadal captured a second straight and sixth overall French Open title earlier this month by beating Federer in the final in Paris for a fourth time.
Up next for Nadal will be 24th-seeded Argentine slugger Juan Martin del Potro, who got past 15th-seeded Frenchman Gilles Simon 7-6 (10-8), 7-6 (7-5), 7-5 on Day 6 of the fortnight. Del Potro is a former world No. 4 and former U.S. Open champ.
"When he's healthy, he must be in the top five...so will be a very tough opponent for me. I know that," Nadal said. "I'm not lucky to play against del Potro in the round of 16."
Nadal is 5-3 lifetime against del Potro, including wins in Madrid and Indian Wells this season. The 6-foot-7 Argentine upset the Spaniard in the U.S. Open semifinals two years ago.
"Of course on Monday I play against the best player in the world in this moment. It will be a big challenge," del Potro said. "You should play everything perfect, and then maybe you have a little chance."
The 24-year-old Djokovic improved to an amazing 44-1 this season by holding off a game Baghdatis, who reached the final four here back in 2006. The match ended after 3 hours, 15 minutes when the Serb converted on his third match point as Baghdatis sent one final forehand long.
Djokovic, who smashed his racquet on the court in frustration at one point, broke Baghdatis three times, while the Cypriot settled for only one break in the tough setback.
"To pull out a win out of this match is great," Djokovic said. "It was great to be part of such an exciting match."
The 2011 stalwart Djokovic will battle lefthanded Frenchman Michael Llodra on Monday.
Federer, meanwhile, improved to 11-8 lifetime against his former nemesis Nalbandian, who, as he often is, has been slowed by injuries this season. The Swiss icon popped 14 aces and was only broken once en route to victory.
"A guy who can beat me eight times knows how to do it nine times, and that's why I'm really pleased to come through," said the 29-year-old Federer, who has yet to lose a set through three matches.
The former world No. 1 Federer owns a men's record 16 major titles, including six of the last eight here at Wimbledon. He's also the all-time leader in grass-court titles (11) in the Open Era (since 1968).
Up next for Federer will be 18th-seeded Russian Mikhail Youzhny, who came back to dismiss 16th-seeded Spaniard Nicolas Almagro 4-6, 6-3, 7-6 (7-3), 6-3.
A big upset came when rising Aussie Bernard Tomic tackled an ailing Robin Soderling in straight sets, 6-1, 6-4, 7-5. The fifth-seeded Soderling is a two-time French Open runner-up.
The 18-year-old Tomic, who is considered to be one of the brightest young players on the ATP World Tour, posted his upset in 1 hour, 52 minutes by stroking 13 aces and holding his big serve throughout. The young Aussie broke his sluggish Swedish counterpart four times.
Tomic will face Belgian veteran Xavier Malisse on Monday.
Sixth-seeded Czech Tomas Berdych, who also has yet to lose at set, improved to 9-1 in his last 10 matches at SW19 with a 6-2, 6-4, 6-3 spanking of American Alex Bogomolov Jr., while seventh-seeded Spaniard David Ferrer leveled Slovakian Karol Beck 6-4, 6-3, 6-3. Berdych gave way to Nadal in last year's Wimbledon finale.
Meanwhile, Poland's Lukasz Kubot upended ninth-seeded Frenchman Gael Monfils 6-3, 3-6, 6-3 6-4 and 10th-seeded American Mardy Fish was leading Robin Haase 6-3, 6-7 (5-7), 6-2, 1-1 when the Dutchman retired from the bout. Fish will tangle with Berdych in the round of 16, while Kubot will encounter Spaniard Feliciano Lopez, who ousted three-time Wimbledon runner-up Andy Roddick here on Friday.
The 29-year-old Fish is the last American man still standing and will appear in the second week at Wimbledon for the first time in his career.
Twelfth-seeded Frenchman Jo-Wilfried Tsonga whipped former top-five star Fernando Gonzalez 6-3, 6-4, 6-3. Tsonga unleashed 29 aces in the easy win.
The Chilean "Gonzo" recently returned to action after recovering from hip surgery.
The former Aussie Open finalist Tsonga should have his hands full with Ferrer on Monday.
The aforementioned Malisse recorded a mild upset by taking out 11th-seeded Austrian Jurgen Melzer 7-6 (7-5), 6-3, 6-0. The capable Malisse was a Wimbledon semifinalist nine years ago.
One other result saw a 19th-seeded Llodra level Taipei's Yen-Hsun Lu 6-3, 6-3, 6-1.
All eight fourth-round matches will be staged on Monday, as Sunday will mark the traditional off day at the All England Club.
Fourth-seeded British favorite Andy Murray will tangle with nifty 17th-seeded Frenchman Richard Gasquet in the round of 16. Murray was this year's Aussie Open runner-up to Djokovic and appeared in the Wimbledon semifinals the last two years.