That hasn’t always been good news for the US sprinters. No longer are the powerful Jamaicans the only threat, either.

Unknowns are bursting onto the scene at this meet that sets the stage for next summer’s London Olympics, stealing attention from American stars such as Allyson Felix and LaShawn Merritt.

The 400 meters was supposed to be Felix’s race, the first leg of a difficult double that would culminate with her trying to win a fourth straight 200 title.

But an unheralded Amantle Montsho of Botswana used a strong finish to beat Felix at the finish and leave the American wondering whether she will even go for the double in London.

Kirani James, a teenager from tiny Grenada, then unseated Merritt as champion in the men’s 400 with a lean at the finish line.

Merritt is hardly race sharp, as he’s coming off a 21-month suspension for doping. He still has plenty of time to get back into elite form to compete in London, provided, of course, he’s even eligible.

He has to wait on a verdict from the Court of Arbitration for Sport on the IOC’s “six-month rule,’’ which prevents athletes who receive doping bans of more than six months from competing at the next Summer or Winter Games. A decision is expected to be rendered in late September.

Usain Bolt, the biggest star in track, is ready to look ahead, too. Yet even after he false started in the 100, the US failed to win gold. Once Bolt was disqualified, another Jamaican, Yohan Blake, kept the title for the Caribbean island. Walter Dix couldn’t close the gap and settled for silver.

Tyson Gay (hip) will be returning in London after sitting out at the worlds. But so will Asafa Powell (groin), and don’t count on Bolt false-starting there.

The world’s fastest man will be eager to atone for his mistake, a process that will start tomorrow in the first round of the men’s 200, while it’s America’s Carmelita Jeter who will be going for a surprising sprint double.

Hardly a surprise, the Americans are in the mix at the top of the medal standings with nine overall, one fewer than Russia. The Russians won two yesterday in the only event on the program, the women’s 20-kilometer walk. Olympic champion Olga Kaniskina won the race and teammate Anisya Kirdyapkina was third.