Two hours before Game 1 of the American League Division playoff series against the New York Yankees on Tuesday night, the young A's were anything but uptight. Several players, notably first baseman Jason Giambi and right fielder Matt Stairs, staged an impromptu throwing contest. The object was to toss a baseball from the third base coaching box through an open luxury box window just below the third deck. All failed, although Stairs' attempt caromed off an adjacent closed pane.

Just because Oakland hadn't been to the playoffs since 1992 and only two starters -- Matt Stairs and second baseman Randy Velarde, boasted playoff experience -- didn't mean it was star-struck. The A's proved it in prime-time by beating the two-time defending World Champion Yankees 5-3.

"There's no question they're playing with a lot of enthusiasm and confidence right now,'' said manager Joe Torre. "They play without fear.''

Not only were the A's on home turf, they closed the regular season as the hottest club in baseball, going 21-7 in September to overtake Seattle for the AL West title. Turns out there was nothing fluky about their finish.

Ramon Hernandez drives in two, including the go-ahead run in the sixth inning.(AP)

Conversely, the Yankees staggered into the postseason with seven consecutive defeats, their longest losing streak since 1995. They dropped nine consecutive on the road and struggled in close contests, falling in 20 of 21 games when scoring three runs or less.

That said, manager Joe Torre remained confident his troops could flick the switch Tuesday night at the Network Associates Coliseum. He should know, being the first manager since Casey Stengel from 1949-53 to guide the Yankees to five consecutive playoff berths.

Coming in, New York had thrived on playoff pressure, winning 22 of its last 25 games. Plus, Yankees players are too proud and well-compensated to roll over. And owner George Steinbrenner is shelling out big bucks -- $110 million, while the A's payroll is a paltry $32 million.

Granted, any roster that includes Derek Jeter, Paul O'Neill, Bernie Williams, David Justice, Roger Clemens and Andy Pettitte, can be intimidating. Oakland might be young, brash and naïve, but it also lost six of nine regular-season meetings.

It didn't take long for the jitters to surface. In the top of the first, A's pitcher Gil Heredia surrendered a leadoff single to designated hitter Chuck Knoblauch, who went to second when the ball hit center fielder Terrence Long in the knee and rolled to the fence. Then Heredia, making his first playoff start, hit Jeter with a pitch, putting runners on first and second with nobody out.

Many of the noisy sellout crowd of 47,360 had barely settled into their green seats, but order was restored when Heredia induced O'Neill to bounce into a double-play and struck out Williams.

"I thought the key for him was getting out of the first inning without damage,'' A's manager Art Howe said of Heredia. "That was huge for us.''

Clemens, 38, making his 13th playoff start, retired the first two A's he faced, then issued back-to-back walks to Giambi and Ben Grieve. But Clemens escaped by getting hot-hitting shortstop Miguel Tejada to foul out to first base.

The last time Clemens and Heredia opposed each other was opening night in 1999. Heredia held up well against his one-time idol, helping Oakland record a 5-3 victory. But this was Game 1 of the AL Division Series, a contest many felt critical in determining whether the A's were serious contenders or pretenders.

"I mean, he's awesome,'' the 35-year-old Heredia said. "I actually have his baseball card in my locker.''

Heredia encountered further difficulty in the second inning and this time, the Yankees roughed him up. Catcher Jorge Posada lined a two-out single to right off the out-stretched glove of Giambi, then scored on a ringing double to left by second baseman Luis Sojo. Third baseman Scott Brosius plated Sojo with a seeing-eye double down the left-field line to give Clemens an early 2-0 cushion.

In fairness to Heredia, he didn't request the ball for Game 1. Oakland manager Art Howe would have preferred to use 20-game winner Tim Hudson, the ace of his staff. However, Hudson threw eight clutch shutout innings in Sunday's division-clinching victory against Texas and won't pitch until Game 3 in New York.

With 260 career victories, Clemens seldom needs a head start. He won seven of his past nine outings during the regular season and finished second in the AL with a 3.70 ERA, striking out 188. Clemens fanned five through four innings Tuesday night and seemed in total control. The only hit he permitted was an infield single to Long in the third inning.

The A's finally nicked Clemens in the fifth. Third baseman Eric Chavez led off with a sharp single and advanced to second on a walk to designated hitter Jeremy Giambi, Jason's younger but not-so-little brother. Catcher Ramon Hernandez, the ninth batter in the order, singled to right to drive in Chavez, then Velarde singled in Giambi to tie the game.

"Ramon's our secret weapon,'' Howe said.

With Jason Giambi at the plate, Clemens was charged with a wild pitch, the ball slipping under the glove of Posada and looking very catchable, and Hernandez trotted home with the go-ahead run. With one out and two on, Clemens avoided further damage by getting left fielder Ben Grieve to bounce into a rally-killing double play.

Oakland's lead was short-lived. In the top of the sixth, Williams opened with a double into the right-field corner and later scored on a sacrifice fly by Tino Martinez.

Not to be outdone, the scrappy A's regained the advantage with a two-out uprising in the bottom of the inning. Chavez and Jeremy Giambi singled, then Hernandez delivered again, ripping an RBI-double into the right field corner. Giambi also attempted to score, but was nailed at the plate on a perfect relay from Martinez to Posada.

"The bottom of their order beat our brains out,'' said Torre.

Velarde agreed.

"They carried us,'' he said. "Hopefully, we can do our part tomorrow.''

The A's added an insurance run in the bottom of the eighth thanks to an RBI-single by Chavez. They didn't need it, closer Jason Isringhausen setting down the Yankees in order in the ninth.

Now, the heat is on New York. If Pettitte doesn't come through Wednesday night, the Yankees must beat Hudson on Friday to stay alive. Don't count on it.