It took a second-half surge, improved free throw shooting and dominant rebounding for the Spartans (11-2) to claim their 11th straight win, 90-81 over the Mountain Hawks.
"I told our team the other day that they were pretty good," Izzo said of the Lehigh (9-4), which had won nine of its previous 10. "They were a little better than I thought."
Keith Appling scored 19 points, including all 12 of his free throws, and had seven rebounds for Michigan State. He was 3 for 13 from the field but made up for that in other ways.
So did Draymond Green, who added 16 points and 10 rebounds for his seventh double-double this season. The three-year captain was 7 minutes late for a morning meeting and didn't start the game. But despite a 5-for-17 performance from the field, he made an impact with a career-high six blocks.
"One thing we said is we want to improve every night," Green said. "It may not have looked like we improved tonight, but this is one of those games where it was probably our first ugly win. The entire win was just ugly."
"It's kind of how I've played here," Thornton said. "My job is to bring the energy. That's just how I always have been. ... I'm just glad we got the win."
"I'm proud of the fight we put forward," Mountain Hawks coach Brett Reed said. "I thought we played together. I thought we hustled. And we tried to make the right plays. ... In order to win this game, we would've had to play near-perfect."
Lehigh shot 42.4 percent from the field to Michigan State's 40.3, but the Spartans -- last in the Big Ten in free throw percentage -- hit 82.1 percent at the line and had a 50-31 edge on the boards.
"We knew we weren't an awful free throw shooting team," Green said. "We had nights where the focus level probably wasn't there. But we definitely focused hard these last couple days in practice."
The Mountain Hawks trailed 11-5 before an 11-0 run gave them a five-point lead. Greiner, a Michigan native, scored nine of those points, including a pair of 3s.
"It was always a dream of mine to play for coach Izzo or play against him," Greiner said. "I got to play against him, and I had a great time. It was a dream come true. I just kind of made open shots, and that's what I wanted to do."
The Spartans drew even a few minutes later, and the lead went back and forth the rest of the half. Michigan State finished with five straight free throws for a 35-33 edge, only to go three down in a hurry.
With a foul to give, freshman Brandan Kearney fouled McCollum well away from the basket with 4 seconds left. But a vigorously disputed continuation call by official Tom O'Neill gave McCollum the basket and three free throws, including two for a technical foul on Izzo.
Lehigh outscored Michigan State 15-0 from beyond the arc in the first 20 minutes, going 5 for 12 while the Spartans were 0 for 2. That more than negated the hosts' 26-14 rebound advantage.
Michigan State quickly tied the game in the second half, then took a 45-41 lead on free throws by Thornton and Green, the first two coming after a technical on Reed.
When Thornton hit the Spartans' first 3 of the night with 13:10 left, the lead swelled and Travis Trice made it a seven-point game from deep a minute later. After a steal, Trice fired a long pass to Brandon Wood for a layup and a nine-point cushion.
A three-point play by Dawson made it a 13-point game and ended any thought of an upset. But Michigan State was left with plenty to work on before unbeaten Indiana visits Breslin Center next Wednesday in its conference opener.
Lehigh also returns to action next Wednesday with a game at St. Peter's.