They say that every dog has his day, and that was certainly the case yesterday. Through nearly two weeks of the Olympic men’s basketball tournament, you couldn’t find a bigger dog than Stephon Marbury. He had made just six of 30 shots on the tournament, played phantom defense, and was a major contributor to the Americans’ stunning inability to score.

That changed with shocking speed in Team USA’s 102-94 quarterfinal win over Spain yesterday. Marbury didn’t just play well – he was awesome.

The Knicks’ point guard and Coney Island native set an American Olympic record by torching the Spaniards for 31 points, breaking the previous mark of 30 posted by Charles Barkley in 1992 and Adrian Dantley in 1976.The big shocker was Marbury’s shooting. He hit six 3-pointers on the game, part of an effort that saw the normally scattershot Americans nail 12 of 22 attempts from downtown.

“They were very good on 3’s.That was something new in this tournament,” Spain’s Pau Gasol told the Associated Press. “They looked motivated, and it’ll be hard to beat them if they keep playing like that.”

It wasn’t just the quantity, either – it was the quality. Marbury hit his shots when they counted the most, snuffing every Spanish rally with big shots down the stretch.

The biggest came with four minutes left and the Americans clinging to an 82-78 lead. With Spain coming down court on a 2-on-1 break, Marbury baited the dribbler into a crosscourt pass that he intercepted, then coolly drained a 3-pointer at the other end to give the Americans a seven-point bulge.

While some may credit the improved shooting to regression to the mean – really, Marbury couldn’t have done any worse – he also helped himself with some hard practice the day before. Marbury spent 90 minutes on the Americans’ off-day practicing shooting from the international 3-point distance, which is three feet shorter than the NBA’s.

“I just got back into my groove, shooting the ball the way I knew how to,” Marbury said afterward.

But what must have had Isiah Thomas jumping for joy came later. With a minute left in the game, Spain pulled back within five points at 91-86 by intercepting a soft inbound and nailing a quick 3-pointer. The U.S. needed a score at the other end, and the ball ended up in Marbury’s hands. He faked right, drove hard to his left, and put in a soft left-handed layup to close the book on Spain.

Seasoned Knicks observers will note that Marbury went to his left about as often as Bill O’Reilly last season, and that it was the major thing Thomas told Marbury to work on in the offseason. He showed yesterday that he had heeded the lesson.

With the game in hand, the only remaining drama was the internationally televised post-game altercation between head coaches Larry Brown of the U.S. and Mario Pesquera of Spain. Pesquera threw a hissy fit after he felt Brown showed up his team by calling a timeout with 23 seconds left and an 11-point lead. The best thing Brown could fire back with was a juvenile “don’t you point at me,” which was unfortunate because he wasted perhaps the only opportunity in his life to talk smack about the Spanish-American war.

Despite Marbury’s play, the Americans had to struggle for all they had to get the win. The 102 points obscured a soft defensive effort – Marbury included – that allowed the normally low-scoring Spanish team to net 94 points.

The Americans again were hurt by fouls, although at least in this game most of the sketchy calls by the international refs went against Spain rather than the U.S. The American NBA players also hurt themselves by continually putting forearms on post players, which is a no-no in the international game. Spain stayed close thanks to a huge game from Gasol (29 points), who destroyed Lamar Odom in the post.

The Americans advance to play Argentina, who knocked off Greece 67-62 in a defensive battle yesterday. Argentina has already beaten U.S. pros once, in the 2002 World Championships, so they have the Americans’ attention.

With pros like Manu Ginobili of the Spurs, Chicago signee Andres Nocioni, and Detroit rookie Carlos Delfino, they’ll provide a tough test for the U.S. to make the final. But as long as Marbury doesn’t revert to his dog status of the previous five games, the U.S. should have enough to get by the South Americans.

In today’s other semifinal, Lithuania will take on Italy. Lithuania advanced with an easy win against overmatched China, 95-75, behind 32 points from sharpshooter Arvydas Macijauskas. China got 29 points from Yao Ming, who spent most of the game watching in horror as his teammates launched more 3-pointers than 2-pointers.

Italy – and perhaps the karma gods – struck down Puerto Rico 81-70 in their quarterfinal yesterday. The Puerto Ricans had intentionally lost their final pool game to get the matchup, only to be let down by their role players. Guards Carlos Arroyo and Larry Ayuso combined for 47 points but the rest of the team mustered just 23. The more balanced Italians got 23 points from Massimo Bulleri and 15 points and 12 boards from Denis Marconato.