Charlie Guevara scored on a rebound one minute into the second half as No. 1-ranked Duke defeated George Mason, 2-0, today in the quarterfinals of the NCAA soccer playoffs.

The Blue Devils (21-0-2) advance to the final four and will play Connecticut, which defeated Long Island, 1-0, on a penalty kick, at an undetermined site. The sixth-ranked Patriots finished with a 19-2-0 record.

In the other semifinal match, Indiana, which defeated Philadelphia Textile, 2-0, today, will play Southern Illinois-Edwardsville, which beat San Francisco, 1-0, Saturday.

After a scoreless first half in which both teams were slowed by a driving rain and a muddy field, Duke took the lead at 46:24. Freshman forward Tom Kain lofted a 20-foot shot that goalkeeper Ken Bernstein blocked but could not hold. Guevara, who attended W.T. Woodson High School in Fairfax, pounced on the loose ball and kicked his eighth goal of the season into the open net.

The Blue Devils made it 2-0 16 minutes later off Sean McCoy's right side corner kick. Kain cut in from the left and dove to head the ball off the cross bar into the goal.

"We played well enough to win, but not much better than that," said Duke Coach John Rennie, whose team has been ranked first for seven of the last eight weeks. "We weren't executing well technically. We weren't playing intelligently. The weather tended to be an equalizer, but it affected us technically quite a lot."

The rain, which continued through the first hour, quickly turned the field into a quagmire. Neither team could work the ball on the ground and had to resort to dropping air balls into the box.

Duke kept George Mason pinned in its own end and outshot the Patriots in the first half, 8-2. Duke defender Mike Jefferies, who attended Whitman High School in Bethesda, failed to capitalize on two early scoring opportunities. His left side volley off a corner kick at three minutes was wide right, and at 20 minutes, he broke through the defense but was unable to leap high enough to reach Mike Chapman's right side cross.

Duke threatened once more before the half, as Chapman broke in alone on Bernstein, cut left and shot toward the right corner. Bernstein managed to kick the ball away.

"We were taking a lot of chances," said Bernstein, who was repeatedly tested but responded with seven saves. "We were trying to counterattack and they got a lot of shots. But you just can't stop Duke from scoring."

George Mason, which was without starting sweeper Chris Short or left wing Marc LeMair, was forced to play the team's leading scorer, Colin Kerr, at sweeper. Although Kerr played brilliantly on defense, his absence on the front line left the Patriot offense flat.

"We got no play out of our left wings at all," said George Mason Coach Richard Broad, who finally moved Kerr back to forward with 25 minutes remaining. "We planned to move Colin back up front later, but then Duke scored its second goal. We may have waited too long."

The Patriots rallied briefly in the second half and outshot Duke, 7-6. But Duke goalkeeper Pat Johnston, who made six saves, responded with several point-blank stops.