Jimmy Butler feels the Miami Heat eased up after Giannis Antetokounmpo was forced off injured as the Milwaukee Bucks staved off NBA playoff elimination with a 118-115 overtime win on Sunday.

Antetokounmpo was cleared to play late in the day having suffered an ankle sprain in Game 3 of the series, but he appeared to be moving well in the warm-up.

He was sent tumbling by Heat forward Andre Iguodala in the second quarter of Game 4, instantly clutching his ankle after he was left in a heap.

Although the NBA's reigning MVP managed to come back on for a pair of free throws, Antetokounmpo went off again straight after, with the Bucks ruling him out at half-time.

Despite such a blow, the Bucks went on to seal an overtime victory that keeps them alive in the series, having lost each of their first three clashes, and the Heat's Butler thinks they underestimated their opponents once Antetokounmpo had gone.

"Well, it shouldn't affect ours, but I think that we relaxed a little bit," the All-Star said when asked if Antetokounmpo's exit impacted the Heat's mentality.

"We stopped playing basketball the right way. We stopped guarding. We stopped living by our defensive principles. We weren't getting 50-50 balls. We were getting out-rebounded. It was just all bad."

Bam Adebayo added: "I feel like we played like we were up 3-0. That's not giving enough effort, not sacrificing our body, and we ended up losing because we were up 3-0.

"They're a good team, so at the end of the day, we should have played like we were in Game 1, Game 2 and Game 3 ... I feel like we didn't play a maximum effort the whole game."

Khris Middleton became the Bucks' inspiration in Antetokounmpo's absence, ending up with 36 points, eight assists and eight rebounds in 48 minutes on court, while he also sealed the victory with 6.9 seconds left of overtime with a three-pointer.

But he focused on the Greek star, lauding him for even getting on court in the first place.

"We know he was laying it out on the line out there for us," he said.

"His ankle was already in bad shape, and he still went out there in the first quarter in the minutes that, in the first and second quarter, however long he was out there, he gave it his all, and as a team you couldn't do nothing but respect your team-mate for giving his all out there.

"So, we had to have his back tonight, and hopefully we'll have him back again for the next game, but if not, we still have to play as hard as we can.

"We've got to fight every night to keep on playing."