An 18-car crash had a huge impact on the inaugural NASCAR In-Season Challenge, collecting the top two seeds and several other contenders in the five-race bracket for $1 million.

The wreck appeared to begin shortly after a Lap 69 restart with contact between Denny Hamlin, the top seed in the In-Season Challenge, and John Hunter Nemechek, and nearly half the field was collected in the backstretch incident at EchoPark Speedway south of Atlanta.

Among others in the crash at the 1.54-mile oval: pole-sitter Joey Logano, No. 2 seed Chase Briscoe (who won at Pocono Raceway last week), William Byron, Daniel Suarez, Carson Hocevar, Ross Chastain, Kyle Larson, Brad Keselowski, Austin Cindric and Josh Berry.

Christopher Bell and Ryan Blaney already had gone more than 50 laps down in an earlier wreck.

The In-Season Challenge started at Atlanta with 32 drivers with the 16 top finishers in head-to-head matchups slated to advance to the Chicago Street Race.

First-round pairings for NASCAR Cup In-Season Challenge are set

The 32-driver, five-race event, which will pay the winner $1 million, begins this weekend at EchoPark Speedway.

• Dustin Long,

Officially out of the race and eliminated before the end of Stage 2: Logano (who will finish behind Alex Bowman), Chastain (who will finish behind Erik Jones), Cindric (who will finish behind Zane Smith, Berry (who will finish behind John Hunter Nemechek) and Blaney (who will finish behind Hocevar).

Though not officially out, Briscoe (racing against Noah Gragson), Hamlin (Ty Dillon) and Bell (Ricky Stenhouse Jr.) are at major risk of being eliminated.

The In-Season Challenge will be winnowed down to a $1 million champion over races at Atlanta, Chicago, Sonoma, Dover and Indianapolis.