Powell scored a career-high 18 points, leading the Heat to a 95-88 victory over the Chicago Bulls on Tuesday night that snapped a seven-game losing streak.
"We got in such a habit of playing with talent only and thinking that talent was going to take care of the lack of effort," Riley said. "These guys are just unadulterated. Effort is a big part of what our culture is."
It was Powell's first game back with the Heat after getting recalled from the NBA Development League and signing a contract for the remainder of the season. Powell was the MVP of the D-League.
"I didn't know how much I was going to play today," Powell said. "Any time I go out there, I want to be full of energy and bring a boost up."
Powell also grabbed six rebounds and had three assists in 37 minutes as he returned to the Heat for the first time since scoring 15 points on March 31.
The Bulls fell to 30-47 and were officially eliminated from the Eastern Conference playoffs after making three consecutive appearances.
"We need to become a better defensive team," Bulls guard Kirk Hinrich said. "The teams who usually compete for the NBA championship are almost always one of the best defensive teams in the league."
There were high hopes for the Bulls this season after winning 49 games last season before falling to the Detroit Pistons in the Eastern Conference semifinals.
"We've kind of lost our identity to what got us here," Hinrich said. "We kind of lost our edge."
Chicago was up by 11, its largest lead of the game, in the third quarter. But the Heat fought back to take a 60-59 lead, with back-to-back 3-pointers by Powell and Davis sparking a 12-0 run.
"We started the third quarter like we typically do, we weren't ready," Riley said. "We take a timeout and we just kept playing. We played extremely well."
Miami took a 69-67 lead into the fourth quarter when Joel Anthony tipped in a miss by Quinn at the buzzer to end the third, drawing a smile from Quinn.
"It was a lot of fun," said Quinn, who has scored in double figures six straight games. "Obviously, we haven't had as many wins this year as we'd like, so any time you get out there and have success and winning, it's a lot of fun."
After Chris Duhon knocked down a 3-pointer to cut the Heat lead to 76-73, the Heat went on an 8-0 to put the game out of reach. The Bulls were just 6-of-20 in the fourth quarter.
"They wanted it more and played a lot harder as a team," Gordon said. "A lot of their guys are playing just to stay in the NBA, so they definitely had a higher level of intensity than we showed."
A jumper by Davis cut the Bulls' lead to 36-35 late in the first half, but the Bulls responded with a 9-2 run led by Deng, who scored seven points, including a three-point play.