Highlights - Gay dominates the 200m
Tyson Gay stormed to victory in the 200m at the London Grand Prix at Crystal Palace clocking 20.00 seconds.
Gay will be hoping to challenge Olympic 100m and 200m champion Usain Bolt at the World Championships next month.
After Bolt's 100m win on Friday, Gay easily saw off compatriot Wallace Spearmon and Ireland's Paul Hession.
Bolt was also a winner on Saturday as he helped a scratch team win the 4x100m relay with a time of 37.46 seconds - the fourth fastest time in history.
But Gay's performance was the one under scrutiny as he warmed up to defend his 100m and 200m World Championship crowns in Berlin in August.
The 26-year-old is expected to be the closest challenger to the all-conquering sprint-king Bolt, who will be aiming to add the World crowns to his Olympic haul.
My groin has been tight on me, I'm trying to take a little Advil (painkillers) to run through the pain
Bolt will have been watching his rival in the 200m and will know he will face a determined challenge from Gay.
Gay powered through the first 100m before easing up but he still left the rest of the field trailing - Britain's Marlon Devonish was fifth with 20.60 - as he showed no ill-affects from a groin problem that has been troubling him.
"I'm feeling OK," said Gay. "I've been trying to keep under the radar, trying to get through this groin situation I have but I should be OK.
"My groin has been tight on me, I'm trying to take a little Advil (painkillers) to run through the pain. I've got to be tough about it. I don't feel it when I run, it's after.
"I'm just taking it one day at a time, it's just frustrating. Any time a sprinter feels any type of nagging pain they get frustrated and the mind has to get strong again.
"I didn't get to warm up like I wanted to because of the situation but I don't think about limping once the gun is shot, I just run.
"The way I slowed down it would definitely have been 19-something (under 20 seconds)."
Gay and Bolt have not raced each other so far this season, although the American has run the fastest 100m in 9.77s and 200m in 19.58s so far this season.
Asked about defending his 100 and 200m titles in Berlin next month, Gay added: "Right now I'm running on faith and that's more dangerous than anything.
"When I hear the gun and just run, it's just dangerous."
Triple Olympic champion Bolt had said earlier this week he felt Gay could not beat him over 100m.
But the American added: "Of course I don't agree with it, (but) he's supposed to have that type of confidence and right now he has mastered the 100 and I'm still working on it.
"He knows I'm one of the only ones close to either beating him or getting the (world) record. He knows that.
"You could say I shut down 30m out but that's not going to impress him because I'm pretty sure he can do that and run 19 seconds.
"But at the same time I'm not really worried about if he's impressed, if he's not. He's just like me, taking it one day at a time and focusing on the 100m.
"I feel like I haven't proved myself yet until I break the world record. I believe that's what it's all about. Asafa Powell's done it before, he has the potential to do it again, but Usain Bolt right now is the man.
"He deserves all the attention and I like to be under the radar."
Bolt was again the star attraction in the final event of the meet in the 4x100m relay and was the anchor for his scratch Racers TC team as Great Britain finished third with a time of 38.44 seconds.
Bolt, who won the 100 in 9.91 into a headwind on Friday, will now take a break from competition to fine-tune for the World Championships.
The Jamaica team for the event, however, will be shorn of five athletes who tested positive for a banned substance on Friday.
"I don't know what's happening back home, I haven't been following it," Bolt said when asked about the revelations.
"All I know is that we have to wait for the results of the second test."