When the Parnelli team pulled out of Formula One after two races of the 1976 season, Andretti returned to Chapman's Lotus team, for whom he had already driven at the season-opening Brazilian Grand Prix. Lotus was then at a low point, having failed to produce a competitive car to replace 1970's Lotus 72. Andretti's ability at developing a racing car contributed to Lotus' return to the front of the Formula One grid, culminating in lapping the field in his victory at the season ending race at the Mount Fuji circuit in Japan. Since mid-1975 Lotus had been developing the use of ground effect, shaping the underside of the car to generate downforce with little penalizing drag. For his part, Andretti worked at setting up his cars for the races, exploiting subtle differences in tire size ('stagger') and suspension set up ('cross weighting') on each side of the car to optimize it for each track, an approach imported from his extensive oval racing experience in the United States. In 1977, at Long Beach, he became the only American to win the United States Grand Prix West, and the last American as of 2020 to win any US Grand Prix. The Lotus 78 "wing car" proved to be the most competitive car of 1977, but despite winning four races, more than any other driver, reliability problems and collisions with other drivers meant Andretti finished only third in the championship. The following year, the Lotus 79 exploited ground effect even further and Andretti took the title with six wins. He clinched the championship at the Italian Grand Prix. There was no championship celebration because his teammate Ronnie Peterson crashed heavily at the start of the race; he was hospitalised and died that night from complications resulting from his injuries.