Powell matched his season high with 28 points, helping Stanford beat Arizona State 76-70 on Saturday.
"He set an aggressive tone," Stanford coach Johnny Dawkins said. "He showed a little bit of everything of what he can do on the floor. That's a big step for him."
Chasson Randle scored 15 of his 21 points in the second half for the Cardinal (14-7, 5-4 Pac-12), who were coming off a 60-57 loss to top-ranked Arizona on Wednesday.
"Powell is a special player," Sun Devils coach Herb Sendek said. "He's big and he's strong, he's athletic, he's experienced, and he's skilled. He can play inside and out. He seems to me to be a prototype NBA power forward."
Powell, who played with the Canadian junior national team last summer, scored 12 points and recorded three of his game-high five assists in the first 8 minutes of the second half, helping to give the Cardinal a 13-point advantage.
"It was close at halftime and we knew we had to build a lead," Powell said. "We had to come out with an aggressive mindset to begin the second half."
Jahii Carson scored 24 points to lead the Sun Devils (16-6, 5-4), who had their three-game winning streak snapped. Jermaine Marshall added 22 points.
"We were there at the end," Sendek said. "We just have to rebound better.
Stanford outrebounded Arizona State 40-32, including a 15-7 edge on the offensive boards resulting in a 15-4 advantage in second-chance points.
"That was a huge factor," Dawkins said. "The guys did a good job of working the paint and giving us extra opportunities."
Marshall's 3-pointer with just over a minute to play brought Arizona State within 70-67, part of an 18-9 run over an 8-minute stretch.
Powell followed by hitting 1 of 2 foul shots. After Carson, who recorded his 25th game of at least 20 points, missed a 3-pointer, Josh Huestis was fouled on the rebound. He hit both of his shots for a 73-67 Cardinal edge with 36 seconds left.
Anthony Brown was 1 of 2 from the free throw and Marshall hit a 3-pointer at the other end as Arizona State drew within 74-70 with 15 seconds left.
Huestis hit two more free throws to seal the victory.
Jordan Bachynski recorded a pair of blocks for the Sun Devils and has 91 on the season. He needs six to match former Arizona star Anthony Cook for the all-time Pac-12 lead.
There were six lead changes, and four ties, in the first half. The Sun Devils took a 33-32 advantage into the intermission.
Randle hit a 3-pointer with 17:30 remaining to play in the game to break a 34-34 tie, part of a 12-3 run to open the second half.
Randle also converted a three-point play 4 minutes later to put the Cardinal up 52-39, their biggest lead of the game.
Carson hit a long 3-pointer to bring the Sun Devils, who were looking for their first Pac-12 road sweep in four years and their first sweep in the Bay Area in nine years, within five at 67-62 with 3:15 left to play.