Suppose March Madness had twice as many basketball teams — and half of the matchups ended in frenzied overtimes.

This is what the World Cup, the biennial chess competition to choose finalists for the next world championship, looks like.

The 127 players who assembled in Tromso, Norway, this week will play knockout matches until two survivors advance to a 2014 Candidates tourney. The 128th invitee, GM Ahmed Adly, was called up by the Egyptian army and denied a chance to play.

The opening-round matches are just two games long, so most pairings lead to tie-breakers with shorter and shorter time controls.

Most of the favorites didn’t need tie-breakers in the first round. Among the few upsets was America’s Ray Robson’s 2-0 trouncing of Andrei Volokitin of Ukraine.

Four additional US players — Gregory Kaidanov, Larry Christiansen, Conrad Holt and Alexander Shabalov — were eliminated quickly.

Of the 64 first-round matchups, 28 had to go to 25-minute tie-breakers. That’s where Judit Polgar was ousted by the obscure Isan Ortiz of Cuba. In another shocker, 14-year-old Wei Yi of China knocked out Ian Nepomniatchi of Russia.

Women’s world champ Anna Ushenina could have eliminated GM Peter Svidler, who outrated her by 276 points, but she made two blunders in the key game.