They did not have it entirely their way, though, with Games record holder Thiago Perreira of Brazil retaining his 400 medley title ahead of Americans Connor Dwyer and Robert Margalis.

Donahue broke the games record in the morning heats and again in the final in a time of 58.73 seconds. The world record of 56.06 was set by Sweden’s Sarah Sjostrom in July 2009.

The relay team of Madison Kennedy, Elizabeth Pelton, Amanda Kendall and Erika Erndl won gold in three minutes 40.66 seconds, some nine seconds outside the world record held by the Netherlands since 2009. Brazil were second and Canada third.

Julia Elizabeth Smit won the women’s 400 meters medley and Gipson Houching the men’s 400 meters freestyle for two more US gold medals on day one.

Outdoor competition began in warm sunny weather after several days of rain that had threatened but finally did not spoil a magnificent opening ceremony on Friday night in the Omnilife stadium packed with 50,000 spectators.

Police helicopters fly over the venues periodically as part of a huge security operation involving 11,000 officers in a city trying to fend off the drugs-related violence that has gripped cities mainly in the north of Mexico.

Security was increased at the athletes’ village on Saturday, with organizers saying it was for the competitors’ peace of mind.

The first gold medal of the games went to American Heather Irmiger in mountain biking cross country at Tapalpa, a two hour drive into hills outside this western city.

Her compatriot Jeremiah Bishop was unable to make it a double though, finishing third in the men’s cross country behind Colombian winner Hector Paez.

“I’m very excited to be here, I feel proud and happy. It is great to have won the first gold medal for USA,” Irmiger told reporters.

Puerto Rican Kelvin Gonzalez was missing from the men’s event having been withdrawn from the games by his team management for doping. He was positive for the blood booster EPO (Erythropoietin) in recent in-house tests.

There was an upset in the women’s modern pentathlon.

Defending champion Brazilian Yane Marques was dominant in the early disciplines but American Margaux Isaksen took charge in the combined event that closed the competition to win with 5,356 points to 5,260 and book her place in the London Olympic Games next year.

“(Marques) is a great competitor and good friend. I was used to coming after her, but I was lucky to make a comeback in the combined event to win,” Isaksen said.

Ivette Gonda won Canada’s first gold medal in the 46-49 kilo Taekwondo category, beating Peru’s Lizbeth Canseco in the final.

Puerto Rico’s Gabriel Mercedes, Olympic silver medallist in Beijing in 2008, beat home hope Damian Villa in the men’s 54-57 kg class to retain his title.