"For sure," said Bjorn Borg, who uses the phrase "for sure" as if it were the essential prefix to nearly every sentence, "I will have to play better in the next rounds if I am going to win."

For sure, he is right.

The 22-year-old Swede is somewhat lucky to be around for today's start of the second week of the Wimbledon tennis championships.

If he is to attain his goal of a third consecutive singles title, a feat last accomplished by Englishman Fred Perry in 1934-35-36, Borg will have to play much better this week than he did in a sluggish 6-4, 6-2, 6-8, 6-4 victory over Chilean Davis Cupper Jamie Fillol in the third round Saturday.

"I was playing much better last year. I am not exactly at the top of my game yet," said Borg, who trailed Victor Amaya by two sets of one and 1-3 in the fourth set in the opening Centre Court match of Wimbledon's 101st year a week ago.

Most observers thought that, having survived this desperate scare, Borg would immediately pick up his game, as he did after losing the first two sets to Australian Mark Edmondson in the second round last year.

"It was the same thing as against Amaya. Bjorn played only so-so, but he made the shots he needed on the big points," said Lennart Bergelin, the Swedish Davis Cup captain and Borg's coach. "Then he played a little better every round.

"Sometimes you need a tough match to get really tight, you know. The only time I see Bjorn playing really fantastic all the way through was in 1976, when he won Wimbledon without losing a set. I thought after Amaya, he would be much better, but he still has a long way to improve.

"I think maybe the weather has something to do with it. It is depressing for all the players. When the sun is up there, it is a better game. When is is cold and rainy like last week, it is difficult to feel comfortable and loose and to play well, especially on grass courts."

For sure.

Borg's fourth-round opponent today is Geoff Masters' a slender, workmanlike, but unspectacular Austrian who is the defending doubles champion at Wimbledon, with partner Ross Case.

The rest of the pairings in the men's round of 16 are No. 8 seed Sandy Mayer vs. No. 13 Wojtek Fibak, Tom Okker vs. Tom Leonard, No. 6 Roscoe Tanner vs. No. 9 Ilie Nastase, No. 5 Brian Gottfried vs. Tim Gullikson, No. 3 Vitas Gerulaitis vs. Hank Pfister, No. 7 Raul Ramirez vs. No. 16 John Newcombe, and No. 2 Jimmy Connors vs. No. 14 John Alexander.

The women's draw at the same stage is more interesting than it has been in several years:

No. 1 see Chris Evert vs. No. 10 Kerry Reid, No. 5 Billie Jean King vs. No. 15 Sue Barker, No. 4 Virginia Wade (the defending champion) vs. Ruta Gerulaitis, No. 7 Wendy Turnbull vs. No. 12 Mima Jausovee, No. 6 Betty Stove vs. No. 13 Virginia Ruzici, No. 3 Evonne Goolagong vs. No. 15 Regina Marsilkova, No. 8 Dianne Fromholtz vs. No. 11 Marise Kruger, and No. 2 Marthina Navratilova vs. No. 9 Tracy Austin.

The oddsmakers are expecting Borg and Connors to meet in a rematch of their magnificent five-set final of a year ago. Also for Evert and Navratilova to have a return bout of their thrilling final in the Wimbledon tuneup tournament at Eastbourne nine days ago.