Sampras Cashes In on Aces : U.S. Open: He starts fast, then outlasts Lendl in five sets. For Czech star, it is first time in nine years he will not be in final. McEnroe advances.

So far in the U.S. Open, we know this much about young tennis player Pete Sampras:

--His scalp itches. Why else would he continually scratch his head while being interviewed on TV?

--His serve thunders. And it’s bigger than Long Island.

--His upset of Ivan Lendl Wednesday comes as a complete surprise. “I think I’m dreaming,” Sampras said.

--His agent is happy. Said Ivan Blumberg, when asked how much money his client just made him: “Lots.”

More information is forthcoming, such as whether a 19-year-old tennis player from Southern California who dropped out of high school can find peace, happiness and a U.S. Open championship.

Sampras himself doesn’t sound quite sure. “I don’t believe what’s happening now,” he said.

What happened is that Sampras lasted five sets with Lendl, the game’s strongest player, then zoomed ahead, fell behind and came back to reach his first Grand Slam semifinal.

In 4 hours 5 minutes, Sampras served 24 aces and added 27 service winners, saved six break points and scored a 6-4, 7-6 (7-4), 3-6, 4-6, 6-2 victory over the three-time champion.

The stunning victory by Sampras put him straight up against John McEnroe, the 31-year-old left-handed legend who continued an unexpected charge to the semifinals in his 14th U.S. Open.

McEnroe needed 2 hours 14 minutes to complete a 6-1, 6-4, 6-4 quarterfinal dissection of 21-year-old David Wheaton under the lights.

McEnroe, who came back from 1-4 in the third set, said he was not counting on his game to have such an impact at the Open, where he is unseeded for the first time in 13 years.

“I was really hoping for a lot, but not expecting it,” McEnroe said. “Now, having a chance to play Sampras to reach the finals, I’ve really got to feel good about that.”

After taking nearly four months off early in the year, McEnroe thinks that his game is slowly rounding into shape again.

McEnroe’s serve was probably the key to the match. He served four aces and mixed in 15 service winners. But McEnroe, who was positively lethal at the net, also struck 39 winners and committed only 9 unforced errors.

For Lendl, it was the first time in nine years that he had lost a five-set match after dropping the first two sets, and the defeat also ended his streak of playing in eight consecutive U.S. Open finals.

“It had to end sooner or later,” Lendl said. “I wish it never ended, but it ended today.”

Oddly enough, it ended when Sampras came back from 0-4 in the fourth set. Although Sampras lost the set, he broke Lendl’s momentum and reasserted his own brand of play in the match.

“If I had lost that set, 6-1 or 6-2, he could have just gone on to win the match,” Sampras said. “He could have just steamrolled me in the fifth.”

The match turned for Sampras in the fourth game of the fifth set, with Lendl serving at 1-2. Lendl saved one break point, but not a second.

Sampras got a good look at a second serve. He ran around his backhand and drove a forehand down the line for a winner. As the ball bounced away, Lendl could only swing his racket in disgust.

Lendl had only one more chance. Lendl held a break point for 3-4 to get the match back on serve, but Sampras hit a service winner to deuce, then aced Lendl. Sampras held when Lendl returned a second serve into the net. This time, Lendl flung his racket into the air.

“That was it right there, the 4-2 game, me serving--that was the game,” Sampras said. “That was the match. That was it.”

As it turned out, that was it. Now Lendl was serving to stay in the match, but he quickly fell behind, 15-40. Down two match points, Lendl rescued one with an ace, but Sampras ended the match with an overhead down the middle.

The teen-ager from Rancho Palos Verdes threw up his arms, accepted a pat on the back from Lendl and then seemed a bit bewildered by the turn of events.

“I can’t really believe what’s going on,” he said.

Already ranked No. 12, Sampras is certain to crack the top 10 for the first time when the new rankings come out Monday. Sampras, who began the year No. 81, will go higher than the top 10, Coach Joe Brandi said.

“The sky is the limit for him,” Brandi said. “He is top five in three or four years, for sure.’

Lendl was gracious in defeat but cautious in his praise of Sampras.

“He is very talented, he is very flashy, but it depends on the day right now,” Lendl said. “I would caution against making any judgment right now because it may have been just one day, you don’t know.”

Mostly, it was one wonderful day for Sampras. Lendl may have dominated the third and fourth sets when he dictated a baseline game, but Sampras set the tone most of the way.

There wasn’t much that Sampras could not do in the beginning. He won the first set with a ruthless act, breaking Lendl as he served to try to stay even. He saved one set point, but on the second, Lendl batted a backhand into the net while running down a volley Sampras had put in the corner.

Sampras’ luck held out in the second set. He saved break points at 2-2 and 3-3 and one more at 4-4, but when he nudged an easy shot into the net, Lendl finally had earned a difficult break.

Just as quickly, Sampras broke back in the next game, and saved four more break points to hold for 6-5.

After Lendl saved three set points in the next game, they moved into the tiebreaker.

Sampras served the first point, an ace, and finished the tiebreaker with a booming forehand down the line into the corner.

All that was left were three more sets, then into the semifinals. Lendl said he was disappointed by not going further, but he said he knew his pursuit of a Wimbledon title had taken away from his match play to get ready for the U.S. Open.

Lendl played only one hard-court tournament before the U.S. Open, losing his first match to No. 103-ranked Mal Washington in the Volvo International.

“Unfortunately, this summer I have paid for the preparation for Wimbledon,” Lendl said. “I haven’t had enough play. I haven’t felt that comfortable on my ground strokes, or as comfortable as I should be because of lack of hitting.

“(Not) enough ground strokes throughout the 3 1/2 months I was on grass,” Lendl said. “(But) that’s the way we chose, and I’m willing to stick by it.”

Even after 24 aces, Sampras said his serve and the rest of his game may have only experienced “a pretty normal day.”

In the grand scheme of things, it didn’t seem normal at all.