Irwin began the day in a tie for the lead with club pro James Mason but birdied the second and third holes to pull away on a bogey-free day at the TPC of the Twin Cities.
The winningest golfer in Senior Tour history, Irwin finished the 54-hole tournament at 12-under 204, good enough for his first title since March. He had lost a pair of playoffs in his previous three starts.
Mason bogeyed the seventh, eighth and 13th holes as his bid for a second career title hit a road block. He carded a 72, sinking a birdie at the 18th hole to salvage a tie for third at 8-under 208.
Hubert Green, who last week defeated Irwin in a seven-hole playoff, shot a 67 to finish alone in second at 9-under 207. Doug Tewell also carded a 67 and tied Mason for third.
Allen Doyle and Bob Gilder shared fifth at 209.