Centrowitz, a rising senior at Oregon, led the first 600 meters of his heat, then faded to the back of the pack.
"Being in the front I really didn't feel much," Centrowitz told USA Track & Field. "The only time it got real physical was with 500 meters to go and I came on the inside and had to give a little nudge, but other than that it wasn't crazy for me."
At 1,000 meters, Centrowitz began to drive back toward the front of the pack. With 400 meters to go, he slipped through a gap and passed on the inside, taking a lead he would not relinquish. Ethiopia's Mekonnen Gebremedhin was second in the heat, finishing in 3:46.71.
"Whatever happens in finals is going to be a great experience for the future. Winning the semi wasn't really in my plans, it was more like focusing trying to get top three and qualify. Once I found myself in the lead I figured I may as well finish it up and it felt great."
Kenya's Asbel Kiprop won the other heat in 3:36.75.