ANN ARBOR, Mich. -- It was hard for Tom Izzo to pinpoint exactly why Michigan State had so many open shots from 3-point range against Michigan.
All that really matters is the ball went in.
"It's hard to say what went right, what went wrong. We executed pretty well," Izzo said. "When you make shots, everything changes."
Bryn Forbes scored 23 of his 29 points in the first half, part of an early barrage of 3-pointers by No. 10 Michigan State in an 89-73 rout of rival Michigan on Saturday. Forbes made seven of the Spartans' 10 3-pointers in the half, and Michigan State finished 14 of 22 from beyond the arc.
Long known for their rebounding and physicality, the Spartans (20-4, 7-4 Big Ten) have now made 47 3-pointers in their last three games. They beat Northwestern and Rutgers by a combined 65 points and the game against Michigan (17-7, 7-4) wasn't too competitive, either.
"We're obviously a better team with Caris out there," Wolverines coach John Beilein said. "Today, I don't know if it makes a difference."
Denzel Valentine had 21 points, nine rebounds and eight assists for Michigan State.
Forbes made his first five shots, all from 3-point range, as the Spartans raced out to a 32-15 lead. Michigan had problems at both ends, shooting only 8 of 28 from 3-point range for the game as Michigan State shut down guard Duncan Robinson.
Forbes added two more 3s in the final 45 seconds of the first half, and Michigan State took a 44-28 lead into the locker room.
The Spartans have won four straight since a three-game losing streak in mid-January.
"I think we're playing really well right now," Forbes said. "We started clicking again, I'd say."
Michigan is now 1-6 against Top 25 teams, and the losses have generally been decisive. The Wolverines allowed a 25-0 run to end the first half in a home loss to No. 22 Indiana on Tuesday.
"These past two games, teams have just punked us," Irvin said. "We can't let that happen."
The Spartans and Wolverines traded baskets for a little while in the second half. Michigan State eventually went on an eight-point run capped by Matt Costello's dunk that made it 69-42. Afterward, the Spartans' coach couldn't find much to complain about.
"To say I'm ecstatic about the performance would be underserving what we did," Izzo said.
The Spartans have won four in a row over Michigan after losing six of the previous eight in the series. The teams were only scheduled to play each other once this season.
Forbes finished 10 of 13 from the field and 8 of 10 from long distance. He's now shooting 50.3 percent from 3-point range on the season.
Robinson was held to two points, and he was held without a 3-pointer for the first time since the season opener against Northern Michigan. He's slipped to 47.7 percent from beyond the arc after going 2 of 13 over the past three games.
After pulling away in the first half with outside shooting, the Spartans made a concerted effort to get the ball inside early in the second.
"I'm worried a little bit about becoming a 3-point shooting team. I don't want that. I want to be able to shoot 3s," Izzo said. "But we've got to be a balanced team, get it inside, get it outside."
Michigan State: The Spartans made seven of their first eight shots from the field, five of which were from 3-point range.
Michigan: It was Michigan's most lopsided home loss to the Spartans since Michigan State's 91-64 victory in 2001.
Michigan State: Plays at No. 18 Purdue on Tuesday night.
Michigan: Plays at Minnesota on Wednesday night.
Follow Noah Trister at www.Twitter.com/noahtrister
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