Heywood, a senior guard and the only starter for No. 16 Oklahoma not averaging in double figures, scored on a follow shot at the buzzer for a 63-61 victory at Missouri on Monday night.
The outcome was briefly in doubt, although Oklahoma players swarmed a TV cameraman to celebrate and a sellout crowd of 13,545 quietly dispersed.
"I don't know," Heywood said. "I just shot it and then I ran to halfcourt."
Referee Tom Rucker's call that the basket was good was emphatic, and the victory was certified after a check of the replay monitor.
Oklahoma coach Kelvin Sampson said two-tenths of a second remained when the ball left Heywood's hands.
"I thought it was good, I absolutely did," Sampson said.
"That red light behind the backboard, that ball was in flight when the light went on. That's why I had confidence."
Missouri players didn't argue the call.
"I wanted it to be too late, but I knew it wasn't," freshman center Arthur Johnson said. "I wanted to hit somebody in the mouth."
In the only other game involving a Top 25 team Monday, No. 17 Syracuse beat Connecticut 65-60.
Heywood wanted to hug somebody after he rebounded Nolan Johnson's missed shot. Besides matching his season high for points, he hit a baseline jumper with 1:15 left to give the Sooners a 60-58 lead and was 4-for-5 from the field.
"Definitely, this is my biggest shot," said Heywood, who entered the game averaging 3.6 points. "It's a great feeling, a lot of hard work."
Oklahoma (21-5, 10-4 Big 12) has beaten Missouri (17-9, 8-5) six straight times. This time, the Sooners ended the Tigers' 13-game homecourt winning streak.
Missouri led 30-24 at the half, but shot only 29 percent thereafter.
"Down the stretch, we made some plays," coach Quin Snyder said. "But in my mind, we didn't make plays in the heart of the game."
Sampson wasn't that happy with the play of his team, even in victory, noting that the Sooners had to scrap for everything.
"I think it's a mark of a very, very good team, when you don't play your best and still find a way to win," Sampson said. "I've seen Oklahoma win a lot of games on the road the last seven years playing that way."
In the final sequence, Sampson wanted Nolan Johnson, the Big 12's leading free-throw shooter entering the game, to try to draw a foul.
"Jameel was at the right place at the right time," Sampson said. "But you know what, he's made that shot this whole conference season."
Wesley Stokes tied it for Missouri with a runner from the baseline with 17.5 seconds to go. The Tigers never got the ball back.
"Our deal at the end was we didn't want Missouri to get a shot," Sampson said. "We were either going to win it or go to overtime."
J.R. Raymond had 13 points and Hollis Price 12 for Oklahoma, which has won nine of 10 overall after a 1-3 start in conference play. This was the final road conference game for the Sooners.
Reserve Clarence Gilbert scored 16 points for Missouri, but was only 5-for-19.
"I had a lot of good looks," Gilbert said. "Some rolled in, some rolled out."
Missouri fell to 2-5 against ranked teams, with two of the losses in overtime.
An unlikely source of offense, reserve Johnnie Parker, helped Missouri take the lead at the half.
Parker, averaging 1.6 points with a previous season high of five points, outscored Oklahoma 6-4 the last 4:41 of the half.
No. 17 Syracuse 65, Connecticut 60 Preston Shumpert broke out of a two-game shooting slump, hitting a school-record eight 3-pointers and scoring 34 points as Syracuse held off Connecticut.
Syracuse (20-6, 8-5 Big East), which lost three of its previous four, never trailed and gave Jim Boeheim his 23rd 20-win season in 25 years as coach. Connecticut (17-9, 6-7) lost for only the second time in its last six.
Albert Mouring led the visiting Huskies with 17 points.