Djokovic, the winner of six major titles, seeks to become the eighth man to complete a career Grand Slam.
He eased past the 35-year-old Haas, winning 40 of his first 43 service points. Haas found himself on the verge of pulling even at 5-all in the tiebreaker, but Djokovic smacked a backhand winner to end a 24-stroke rally longest of the match and won the next point as well for a two-set lead.
Djokovic reached his 12th consecutive Grand Slam semifinal. He improved to 33-4 this year.
Nadal, seeded No. 3, turned in his finest performance of the tournament yet. After dropping the first set in each of the first two rounds, he has won 12 sets in a row, looking better and better at Roland Garros, where he now is 57-1.
Nadal improved to 10-0 against Wawrinka and has won all 22 sets they've played. The Spaniard is trying to become the first man to win eight titles at the same Grand Slam tournament.
Defending champion Maria Sharapova needed a comeback unlike any other in her career to reach the semifinals, rallying past Jelena Jankovic, 0-6, 6-4, 6-3.
It was Sharapova's first win after losing an opening set 6-0. Her opponent Thursday will be two-time Australian Open champion Victoria Azarenka, who reached her first Roland Garros semifinal by beating Maria Kirilenko 7-6 (3), 6-2.
The No. 2-seeded Sharapova earned her first French Open title a year ago to complete a career Grand Slam. She has won 12 matches in a row at Roland Garros, where her 42-9 record is the best among active women.
"Obviously it only gets tougher from here," Sharapova said, "but I'm really happy I'm at this stage again."
She's 5-7 against No. 3 Azarenka.
"It's our first meeting here," Azarenka said, "so it's definitely going to be exciting and interesting."
No. 1 Serena Williams, seeking her first French Open title in 11 years, plays 2012 runner-up Sara Errani in the other semifinal Thursday. The other men's semifinal Friday will match Spaniard David Ferrer against Jo-Wilfried Tsonga, who seeks to become the first Frenchman in 30 years to win Roland Garros.
The warmest weather of the tournament greeted the last of the quarterfinalists, and Jankovic quickly had Sharapova sweating. In the first set the Russian repeatedly missed the lines by narrow margins or clipped the net cord, and the match was 35 minutes old before she won a game and only then because Jankovic double-faulted on break point.
Jankovic won 27 points in the first set, 20 on unforced errors by her opponent.
"I still felt like I was in the match," Sharapova said. "And I was."
She then began to find her range while hitting even harder than before, while Jankovic did her best to withstand the barrage. In contrast to Sharapova's metronomic shrieking, Jankovic went about her business in silence until she started muttering to herself as her lead disappeared.
"It was a big fight," Jankovic said. "It was great tennis out there. We battled."
Sharapova earned the first break of the final set to take her first lead at 4-3. Toward the end the rallies became longer, and she won the majority, often by hitting shots at improbable angles.
Twice Sharapova yanked lunging backhand returns cross-court for winners. She finished off another point with a forehand struck so violently her necklace flew into her face.
"It was certainly nice to change things around," Sharapova said, "because I wasn't doing much in the first six games."
When Jankovic's final shot sailed wide, Sharapova responded with a slack-jawed smile, as though she couldn't quite believe her comeback. She had dropped a first set 6-0 five other times in her career and went on to lose each match.
Most of her results this year have been less stressful. She's 35-4, with all but four of those matches decided in straight sets.
Azarenka is 27-2 and enjoying her best run in eight appearances at Roland Garros. She needed 76 minutes to take the grueling first set against Kirilenko, and the Belarusian improved her record this year in tiebreakers to 4-0. The second set went more quickly, with Azarenka losing only six points in four service games.
Azarenka advanced to the semifinals at her fourth consecutive major event.