Sullivan would set the pace at Indy again in 1988, qualifying second and leading 91 of the first 101 laps. Sullivan was part of the all-Penske front row with teammates Rick Mears and Al Unser Sr. A wing adjuster broke on Sullivan's car just after the halfway mark, and his car hit outside wall in turn one, ending his day. Nevertheless, he rebounded, posting finishes of 4th or better over the next six races, winning at Portland and the Michigan 500. The win at Michigan completed a career Indy car Triple Crown (Indianapolis, Michigan, Pocono). He finished the season with five top-5 finishes over the final five races, including two wins. At the second-to-last race of the season at Laguna Seca, Sullivan won the pole position, led the most laps, and won the race. With still one race remaining, Sullivan clinched the 1988 CART championship, holding an insurmountable 35-point lead. It was Sullivan's first championship title and Penske's first since 1985.