Ten years ago, when he was seeded in the first Wimbledon tennis championships open to professionals, Tom Okker was known as "The Flying Dutchman." This year, at age 34, he seemed to have no wind left in his sails, and appeared as cursed as the famous ship from which his nickname came.

On another blustery English afternoon, Okker played superbly yesterday to defeated Ilie Nastase, 7-5, 6-1, 2-6, 6-3, and reach the Wimbledon singles semifinals for the first time. In 12 previous appearances in the oldest and most prestigious of tennis tournaments, he had three times reached the quarterfinals (1968-69-75), but never gone further.

Okker is the only gate-crasher in the final four. Alongside hime in tomorrow's semis will be the three top seeds, Bjorn Borg, Jimmy Connors and Vitas Gerulaitis.

Borg, 22, the Swede who has a chance to become the first man since Fred Perry in 1634-35-36 to win three consecutive singles titles here, escaped trouble in the first two sets yesterday to oust eighth-seeded Sandy Mayer, 7-5, 6-4, 6-3, on Centre Court on the All England Lawn Tennis and Croquet Club.

Connors again looked like the lean and hungry champion of 1974 as he ravaged seventh-seeded Raul Ramirez, who had not lost a set in the previous four rounds, 6-4, 6-4, 6-2.

Gerulaitis, eager to break into what he calls the "two-mile high club" which currently has only Borg and Connors as members, came back from 2-4 in the third set to oust fifth-seeded Brain Gottfried, 7-5, 4-6, 9-7, 6-2.

Gerulaitis, who last year took Borg to 8-6 in the fifth set in by far the best match of the centenary Wimbledon, is paired against Connors in the semis this time. Borg, who snared the title without losing a set in 1976 and last year beat Connors in a final of brutish majesty, plays Okker.

Okker has lost in the first round of a dozen tournaments and had won only a handful of singles matches this year coming into Wimbledon. But he played tight, nearly error-free tennis against Nastase, who was far below the form he displayed Monday in upsetting Roscoe Tanner.

"I like to play Nastase, because you get to play a lot of tennis against him." said the quick, nimble, fedgety little Dutchman, who had won nine of 17 previous career meetings with the mercurial Romanian

"He doen't blast you off the court like Tanner or the other big servers can. I was very happy he beat Tanner. Against Nastase, I can get into the points. We have similar games, not power games, and have to maneuver each other around."

Okker was getting the first serve in and dashing to the net for quick and agile volleys. It was his return of serve and passing shots that won him the match, however, as he punished Nastase for missing far too many first serves and hitting short volleys.

Okker darted all over the court, whipping the ball back with his wristy topspin forehand, threading the needle with passing shots and that just eluded Nastase's acrobatic lunges.

He started niggling in the last game of the first set, when Okker hit a winning return off a serve he thought was a fault. He muttered and gestured at photographers, spectators and the bald, bespectacled linesman who made the call, snarling. "We're playing tennis here. Would you mind eaking up?"

At 2-3 in the fourth set, after double faulting to 30-40, Nastase was called for a foot fault on his nexf serve. That rankled him, especially because he promptly muffed a forehand volley - th shot that let him down most throughout the match - for the break.

In his next service game, he told the foot fault judge, "Call as many as you want now. Call 10. It is too late."

Connors was ripping his service returns and passing shots with savage pace, staying low and following through as only he can. Even some of his colleagues were awed. Tim Gullikison, on leaving the competitors stand, marveled, "Did you see that? Geez, Jimmy is playing well."

Connors also was relentlessly aggressive on his own serve, attacking the net at every opportunity, boring in with the style that was once likened to that of "Smokin Joe" Frazier in the ring.

By the end, Ramirez was battered and bewildered. He couldn't believe how many flashing winners Connors hit on the dead run. He took to flipping his racket into the airand catching it, tossing bits of dead grass to the breeze, chatting with spectators - all the gestures of a beaten man trying to enjoy gallows humor at his own expense.

Borg was down a break at 4-5 in the first set with Mayer, a classical stylist who has clean, compact strokes with no wasted motion. But the stolid Swede lifted his game, broke straight back and won three games in succession for the set.

Borg saved two break points at 2-3 in the second set, even though Mayer was returning serve with admirable pace and accuracy.Then he broke in in next game. From 30-15, Mayer pushed a forehand volley long, Borg laced a running forehand down-the-line pass, then lofted a winning topspin lob off a first volley.

Every time Borg was in trouble, he seemed to produce a winning serve or a big point. He could not be intimidated.

"Mentally, he's a giant right now," said Mayer. "He knows what to do on the big points and is calm enough to execute it."

Gerulaitis and Gottfried both that was of consistently high standard, but had a stark qualtiy to it.Gerulaitius soft, dipping returns and passing shots, coupled with his quickness at the net, eventually won out over Gottfrieds better serve and forthright net play.

The crux of the match came in the third set. Gerulaitis lost his serve in the first game, but broke back to 4-4 with a short return that forced a half-volley error. Gottfried saved two set points from 15-40 in the 12th game, and Gerulaitis held from 15-40 in the next game, putting in four good deep first serves when he had to.

Gerulaitis broke for the set in the 16th game Gottfried double-faulted to 30-30. Gerulaitis cracked a backhand return winner, then angled a backhand smash after darting to the net behind a good lob. He never looked back from there.