The 22-year-old Elliott from Dawsonville, Georgia inherited the lead on lap 56 when race leader Kyle Busch was forced to come back down pit road for more fuel.
Martin Truex Jr. has won an action-packed first stage of the Cup race at Watkins Glen, followed by Jimmie Johnson and William Byron, as teams began playing the strategy game early. Elliott took over the lead by passing Busch on lap 27. Elliott pulled out to a half-second lead while Truex was fighting to get back to the front after a restart mired him in 12th. GMS has been using several drivers in its No. 23 vehicle since Spencer Gallagher's suspension in May for failing a NASCAR drug test. Gallagher was reinstated last month, but the team has been using a variety of drivers, including Elliott's son, Chase Elliott, in the auto. He beat AJ Allmendinger by 3.3 seconds. But Truex's No. 78 Toyota skidded, Elliott regrouped and pulled away, and Truex sputtered home, out of fuel.
Busch took charge on the restart, pulling away to a lead of almost three seconds over Truex, with Hamlin third and Chase Elliott fourth. All three of Truex's road course victories were won with strategy, including last year at The Glen and this year at Sonoma in California's wine country. His last Xfinity Series race was in October 2005 at Memphis.More news: UK poised to ask Russia to extradite suspects in nerve agent attack
Denny Hamlin started the race from the pole of the 220.5-mile event but lost the lead on Lap 2 when he was passed by teammate Busch in the sweeping Carousel turn.
Hamlin traversed the 2.45-mile layout at 125.534 miles per hour in qualifying on Saturday, just ahead of series points leader Kyle Busch.
After eight runner-up finishes, Chase Elliott outdueled the defending champ this time en route to his first win, coming in his third full-time season and his 99th start in the Monster Energy NASCAR Cup Series.
Chase Elliott (9) leads the pack around Turn 1 during a NASCAR Cup Series auto race, Sunday, Aug. 5, 2018, in Watkins Glen, N.Y.
Both of these statements are set to change on Saturday, August 25, as Elliott, 62, is set to return to NASCAR in the Xfinity Series race at Road America.