LAS VEGAS -- Lennox Lewis has his championship belts back. Now he wants Mike Tyson.

"Since the Evander Holyfield fight (in 1999) I've been waiting for Tyson," Lewis said Sunday after regaining the WBC-IBF heavyweight titles on a fourth-round knockout of Hasim Rahman.

The 36-year-old Lewis might not have to wait much longer.

Talks are well under way for a Lewis-Mike Tyson fight in early April, a source close to the negotiations told ESPN's Brian Kenny.

HBO president Ross Greenburg said he is committed to making a Lewis-Tyson fight happen.

"We will negotiate with our brethren at Showtime," he said.

Tyson congratulated Lewis for recapturing the title.

"He said he wants me," Tyson said. "Well, I really look forward to it."

Lewis has a multifight contract with HBO, while Tyson is tied to Showtime.

"We already have had many discussions with Showtime and now it's time to make it happen," Greenburg said.

Making it happen probably would be easier without Don King, who promoted Saturday night's rematch at Mandalay Bay.

Rahman has a multifight deal with King, but Lewis had a contract with the promoter only for Saturday's match.

Lewis called King "a truly great promoter," but Tyson has said he would not fight again for King. He and King are suing one another.

In boxing, however, yesterday's enemies are today's friends, especially when megabucks are involved.

The 35-year-old Tyson, a former undisputed champion, is expected to fight Ray Mercer on Jan. 19 at a site to be determined. The match has not been announced officially.

John Ruiz is the WBA heavyweight champion, and will defend his title in a third bout against Holyfield on Dec. 5 at Foxwoods Resort Casino at Ledyard, Conn. Lewis had become undisputed champion by outpointing Holyfield, but was stripped by the WBA for not giving Holyfield a rematch.

A Tyson fight would be a mandatory WBC title defense for Lewis.

Lewis appeared headed for a Tyson bout when he was upset by Rahman on a one-punch knockout in the fifth round April 22 in South Africa.

Lewis admittedly took Rahman too lightly in that fight. Not this time.

"When we went to camp, everybody was focused and they kept me focused," Lewis said.

The first two rounds were a battle of jabs. Lewis than hurt the 29-year-old Rahman with a couple of rights to the head in the third, and shook him with another right 20 seconds into the fourth round.

The end came at 1:29 of the fourth, when Lewis landed a left hook and crashing right to the jaw that dropped Rahman flat on his back. He struggled up at the count of 9 but fell again and referee Joe Cortez signaled the fight was over.

"He couldn't handle my movement," Lewis said. "I gave him different looks."

Rahman's championship reign of 209 days was the shortest in heavyweight history -- four days shorter than that of Leon Spinks, who won and lost in fights with Muhammad Ali in 1978.

"He had his 15 minutes of glory," Lewis said. "The titles were on loan. They're now back with me."

Lewis became the third man to win at least a share of the heavyweight championships three times. Ali and Holyfield did it before him.

The fight will be rebroadcast on HBO on Nov. 24 at 10 p.m. ET and PT.

Information from the Associated Press was used in this report.