Thomas posts world-leading 21.60 to claim US women's 200m title
Richardson, coming off a 100m victory on Friday, seized the early lead but Thomas gained ground off the curve to take the victory, with Richardson second in a personal best 21.94 and Kayla White third in 22.01.
Thomas, the Tokyo Olympics bronze medallist, had opted not to run the 100m at Hayward Field in Eugene, Oregon, this week, and the decision looked right as on fresh legs she twice improved on the best 200 time of the season.
She'd clocked a world-leading 21.86sec in the semi-finals, which reigning 200m world champion Shericka Jackson erased with a 21.71 at the Jamaican championships in Kingston.
Thomas responded in a big way, her personal best amping up anticipation for a showdown with Jackson at the World Championships in Budapest next month.
"Right after my world lead I immediately saw that she went better," Thomas said. "And so I'm thinking, OK, it's on."
It was a contrast to last year's US championships, where a tearful Thomas failed to book a World Championships berth as she battled a hamstring injury.
"Coming here last year and being injured was really heart-breaking for me," she said. "I was really ready this year. I was hungry, I wanted it more than, I think, anyone."
Richardson will still have a chance at a sprint double when she contests her first World Championships at Budapest next month.
She was infamously barred from the pandemic-delayed Tokyo Olympics in 2021 after testing positive for marijuana, and then saw her hopes of competing for a medal at last year's World Championships vanish when she bombed out of the US trials.
Knighton wins 200m
In the men's 200, Erriyon Knighton held off Kenny Bednarek to win in 19.72sec with Courtney Lindsey third.
Bednarek and Knighton won silver and bronze behind teammate Noah Lyles at last year's World Championships. Lyles has a bye into the event in Budapest, where he'll be gunning for a sprint double after finishing third in the 100m this week.
Reigning 100m world champion Fred Kerley, however, saw his hopes of a Budapest double evaporate with a fourth-placed finish in the 200.
Christian Coleman, already assured of a 100m berth with his runner-up finish to Cravont Charleston, also missed out in the 200m, finishing sixth.
Shamier Little, who won world 400m hurdles silver back in 2015, claimed her first national title since 2018 with a victory in 53.34sec.
"I'm just not a quitter," Little said of her determination to return to the top of the podium. "Like I'm going to figure it out one way or another."
Dalilah Muhammad, Olympic gold medallist in 2016 and world champion in 2019, was second in 53.53 and Anna Cockrell was third in 54.24.
The three could be joined in the 400m hurdles in Budapest by world record-holder Sydney McLaughlin-Levrone, who posted a dominant win in the 400m flat this week but still has a hurdles by in Budapest and has yet to confirm her plans.
Rai Benjamin won the men's 400m hurdles going away, capturing his fourth national title in a scintillating 46.62 to set up another likely showdown with Norwegian rival Karsten Warholm at worlds.
Benjamin took silver behind Warholm at the Tokyo Olympics -- another silver to go with those from the 2019 and 2022 world championships.
Daniel Roberts won the 110m hurdles in 13.05sec with rising talent Cordell Tinch second in 13.08 and Freddie Crittenden third in 13.23.
It's a dream result for Tinch, who only returned to training in January after a three-year break from the sport and broke 13 seconds in June.
World champion Grant Holloway, with a bye into Budapest, opted not to run the final.
In other events, Olympic and world champion Katie Moon won the women's pole vault with a world-leading 4.90m.
Ryan Crouser easily won the men's shot put with a throw of 22.86m, well off the world record of 23.56 he set in May but plenty to beat Josh Awotunde (22.10).