Phelps' time of one minute 58.24 seconds was good for fourth-fastest in the preliminaries. He said he didn't get back to his room at the athletes village until midnight.
Phelps woke up and checked his Twitter account Wednesday morning, saying he found "thousands of mentions" of his historic accomplishment.
"It was pretty cool," he said, name-checking U.S. President Barack Obama and Spanish soccer player Gerard Pique among his favourite tweets. "I really didn't get much sleep last night. I didn't warm down at all. This morning didn't feel too comfortable."
Teammate Ryan Lochte was second-quickest at 1:58.03 a short time after he advanced in the 200 backstroke heats.
"It was kind of hard stepping up in the morning," he said. "All that celebrating takes a lot of energy out of you. All I had to do was get a lane for tonight, and that's what I did."
Toronto's Tobias Oriwol also advanced in the men's 200-metre backstroke.
Lochte is seeking his first gold in the event. He won the bronze four years ago in Beijing, and was second behind Phelps at the 2004 Athens Games. Phelps is trying to become the first male swimmer to win the same individual event in three consecutive Olympics, although Japan's Kosuke Kitajima has a shot at achieving the feat first when he swims in the 200 breaststroke final Wednesday night.
The 200 IM final is Thursday.
Laszlo Cseh of Hungary, the silver medallist in 2008, led the way in 1:57.20. Kosuke Hagino of Japan was sandwiched between Lochte and Phelps in third at 1:58.22.
"That was much better than in the butterfly," said Cseh, who failed to make the 200 fly final.
Andrew Ford of Guelph, Ont., made the cut for the semifinal by finishing 16th in 2:00.28.
Chad le Clos of South Africa, who out-touched Phelps for gold in the 200 butterfly on Wednesday, advanced to the evening semifinals in 11th. Le Clos was still reveling in his surprise win, having gotten about two hours of sleep.
"I have already watched the race about 10 times," he said. "My friends were waiting for me when I got back to the room and we watched it. It was really awesome, really emotional. I really didn't know it was so close. I didn't think I'd won when I touched."
Tyler Clary and Lochte qualified 1-2 in the 200 backstroke, positioning themselves to extend the American dominance of the event.
Clary won his heat in 1:56.24. Two heats later, Lochte rallied over the final lap to win in 1:56.36 as he tries to defend the gold medal he won in 2008.
"I was happy with how I swam," Clary said. "I was able to swim more like I know I can and not like the nervous wreck I was the last couple of days."
He finished fifth in the 200 butterfly on Tuesday, the same race in which Phelps settled for silver, his 18th career medal.
"I thought it was pretty cool when I woke up this morning and saw he had gotten a tweet from President Obama," Clary said of Phelps, who later earned his record 19th career Olympic medal when the U.S. won the 4x200 free relay.
The U.S. has won the 200 back in the last four Olympics, and finished 1-2 in three of them. Matt Grevers and Nick Thoman earlier claimed the gold and silver medals in the 100 back.
Lochte is looking to get back on track after two disappointing finishes. He won the 400 individual medley in dominating fashion on Day 1 of the swimming competition, then faltered as the anchor of the 4x100 freestyle relay and finished fourth in the 200 free.
Defending Olympic champion Rebecca Soni of the U.S. had the fastest time in the 200 breaststroke at 2:21.40. She earned silver in the 100 breast for the second consecutive Olympics, missing the gold by eight-hundredths of a second.
"It motivates me," she said. "It definitely helps me refocus on the 200 and realize that my strength lies with the longer distance."
Rikke Pedersen of Denmark was second at 2:22.69. Soni's teammate, Micah Lawrence, advanced in fourth. Sara Nordenstam of Norway, the 2008 bronze medallist , finished 23rd to miss the final.
Martha McCabe of Toronto was third in her 200-metre breaststroke heat to earn a spot in the semis.
Zhang Fenglin of China was third-quickest in the backstroke in 1:56.71, followed by Ryosuke Irie of Japan in 1:56.81. Arkady Vyatchanin of Russia, the bronze medallist four years ago, finished 17th, one spot out of the evening semifinals.
Tang Yi of China led the women's 100 freestyle heats, with defending Olympic champion Britta Steffen of Germany back in the pack.
Tang won her heat in 53.28 seconds. China has only won three medals in the event, though two of them were gold in 1992 and 1996.
Melanie Schlanger of Australia was second-quickest in 53.50. World champion Jeanette Ottesen Gray of Denmark was third in 53.51.
Dutch sprinter Ranomi Kromowidjojo moved on in fifth in 53.66. Jessica Hardy of the U.S. advanced to the semifinals in eighth at 54.09. Her teammate Missy Franklin tied for 10th with Sarah Sjostrom of Sweden at 54.26.
"I'm really excited about the 100 backstroke still," said Franklin, who won her first Olympic gold medal in that event on Monday. "I'm saving something for the freestyle."
Julia Wilkinson of Stratford, Ont., was third in her 100 freestyle heat and advanced in 54.16.
Steffen, who swept the 50 and 100 freestyles in Beijing, was 14th at 54.42.
"I hope I can swim better this evening," she said. "I felt a bit flat this morning."
Australia's women topped the 4x200 freestyle relay heats. The team of Brittany Elmslie, Angie Bainbridge, Jade Neilsen and Blair Evans finished in 7:49.44.
The U.S. squad of Lauren Perdue, Shannon Vreeland, Alyssa Anderson and Dana Vollmer was second at 7:50.76. The Americans had won every 4x200 relay since the event began at the 1996 Atlanta Games, but lost the title to Australia four years ago.
Canada qualified third and host nation Britain also made the final.