Making his third and final planned Cup appearance of the season in a Rick Ware Racing Ford Mustang after taking in the Circuit of the Americas rounds and the Chicago road course, Button started 31st in the 39-car field and endured an eventful race to finish a lap down on winner Michael McDowell.
The Briton admitted to making mistakes after having to serve a pitlane speeding penalty and another for overshooting the first corner while chasing Kevin Harvick. He also lost time being turned around by Ricky Stenhouse Jr.
But despite the "disappointing result", in setting the sixth fastest race lap Button said his pace was "really good" and came away satisfied with his improvement over the weekend.
"The pace is there, it’s just that I made mistakes today," said the 15-time F1 race-winner.
"The car was working well. Yesterday was frustrating just because we didn’t have any pace. Today, the guys did a really good job of finding a set-up that worked for me.
"I could brake later, so I could make a lot of moves. I can’t imagine how many cars I actually overtook during the race.
"But at the end of the first pitstop, I was speeding into the pitlane. So, I had to do a drive-through. Kills your race – about 30 seconds in pitlane.
"So, it sets you back a lot, and then when I made a move on someone – I think Stenhouse Jr. – he spun me around and it cost me a bit more time. It wasn’t great.
"Then pushing to the end to chase down Kevin, I locked up and went straight across the grass in Turn 1. So, had to do a stop-and-go.
"It was messy. But, the pace was there. It was really good."
He added: "Just a disappointing result, I enjoyed it. Lots of overtaking, wheel-to-wheel banging as you could probably see by the car.”
Chicago winner Shane van Gisbergen was the best of the international contingent on his second Cup start, the three-time Supercars champion ending up tenth in his Trackhouse Racing Chevrolet run under the Project 91 banner.
The Kiwi, who is expected to move full-time to NASCAR next year after making his first oval start in a Truck Series outing on Friday, admitted he'd expected to find the going tougher on a permanent venue that NASCAR has previously visited relative to the inaugural street race in Chicago.
“It’s hard here because everyone’s on it," said Van Gisbergen, who managed to lead a lap during one of the green-flag pitstop cycles.
"Everyone knows the track and there’s a lot more room for error. Everyone’s racing aggressively.
"So much fun to be back, hopefully, can do more."
In a race that matched the record for most countries represented in a single Cup race (seven), van Gisbergen's Supercars rival and current series points leader Brodie Kostecki qualified 11th, but the Australian had to start from the back of the field after a qualifying crash. The Richard Childress Chevrolet driver steadily marched through the field and finished 22nd.
Standing in for Noah Gragson at Legacy Motor Club, 2010 Le Mans winner Mike Rockenfeller gained 13 positions from the start, finishing 24th in his third career Cup start. He too served a speeding penalty on pit road.
Like Kostecki, Button's former F1 sparring partner Kamui Kobayashi was also making his NASCAR debut and beat Button in qualifying to start 28th.
But he too had a run-in with Stenhouse, as the 2023 Daytona 500 winner barrelled into the Toyota World Endurance Championship ace at Turn 1, with the resulting spin costing Kobayashi several spots as he ultimately finished 33rd.
The Japanese said he "learned a lot" from the experience and was magnanimous about his clash with Stenhouse.
"I got hit by someone, but this is NASCAR," he said.
"But the racing in the field was great. It’s a really cool championship – I had a great experience here."
