Dale Ellis scored off his missed shot with 52 seconds left in double overtime tonight as the Seattle SuperSonics defeated the Houston Rockets, 128-125, and took the best-of-seven NBA Western Conference semifinal series, 4-2. Ellis' basket broke a 125-125 tie. Clemon Johnson added a free throw with four seconds to play after Houston's Ralph Sampson and Robert Reid missed potential game-tying field goals. Seattle will play the Los Angeles Lakers for the conference championship. The best-of-seven series will begin Saturday at the Forum. The SuperSonics were victorious despite a career-high 49 points by Houston center Akeem Olajuwon, who also had 24 rebounds and six blocked shots. Tom Chambers led Seattle with 37 points -- including a crucial three-point play in the first overtime -- and Ellis had 36. The Rockets had a chance to win in the first overtime when Sampson was fouled by Ellis with five seconds to play. Sampson made the first free throw to tie the score, 115-all, but missed the second, producing the second overtime. The SuperSonics had trailed by two before before Chambers' dunk and foul shot with 16 seconds left put them up by 115-114. Seattle overcame a five-point deficit in the final minute of regulation. The SuperSoncis trailed by 107-102 with 55 seconds left before Ellis scored on a short shot in the lane. Then, on Houston's subsequent possession, guard Dirk Minnifield lost the ball to Seattle. Ellis took a pass ahead of the field, scored on a layup and added a free throw after being fouled with 25 seconds remaining to tie the score. Seattle was able to get its big three of Ellis, Chambers and Xavier McDaniel off to a good start in the scoring column. It was the first time in the series that all three -- each of whom averaged more 22 points a game during the regular season -- had it going offensively at the same time. Ellis, a 6-foot-7 guard, scored eight of the SuperSonics' first 10 points as Seattle went ahead by 10-5 in the opening 3:25. That was followed by seven straight points between McDaniel and Chambers, giving Seattle a 17-11 advantage at the 6:05 mark. Houston, however, was getting quality production from its twin towers, Olajuwon and Sampson. Olajuwon hit a pair of free throws with 5:21 remaining in the period to tie the score at 17, and the duo scored six of the Rockets' next 10 points as well, giving Houston a 27-25 lead with 2:09 left. Seattle responded with 11 straight points, four from center Alton Lister and reserve guard Eddie Johnson and a three-point field goal by Ellis. Houston broke the spurt with a free throw by Allen Leavell with 14 seconds left. It was the last point in the quarter, Seattle on top, 36-28. Ellis led the way with 13 period points. It was in the second period that the Rockets made their big push in bidding to become just the fifth team in NBA history to come back from a 3-1 deficit in a best-of-seven series. They scored the first five points of the quarter to close to within 36-33, then bided their time, never letting the SuperSonics score more than four consecutive points. McDaniel scored on a dunk 7:50 before halftime to make the score 44-37, Seattle. But the Rockets took control, going on a 15-4 run that moved that ahead, 52-48, with just over three minutes left. Leading the way was Olajuwon, controlling the backboards at both ends of the floor. Houston was able to maintain its four-point lead, taking a 58-54 advantage into the locker room at halftime. Olajuwon ended the first two periods with 15 points and 13 rebounds, and Sampson and guard Robert Reid had 10 points each. Seattle was led by Ellis' 17 points; McDaniel had 12, Chambers 11. The SuperSonics, who hit 57 percent of their field goals in the first period, cooled off to 42 percent by halftime. They also were getting soundly whipped on the boards, the Rockets holding a 32-17 advantage in rebounding. Entering the second half, many observers were wondering whether the potential first-half altercations would develop into something more substantial. In the opening two quarters, Seattle's Maurice Lucas squared off with Sampson, then with Olajuwon, after Olajuwon jostled the Seattle veteran while interceding. Both were assessed technical fouls after the incident; Sampson wasn't penalized, although he threw a half-hearted punch at Lucas when things began to get heated. Later in the period, Lucas again was in the thick of it, when, after a Houston free throw, he was shoved out of bounds by the Rockets' Jim Petersen. Chambers scored the first points of the third quarter on a pair of free throws, and Lister followed with a layup that made it 58-58, the 11th tie of the game. However, Olajuwon began to reassert himself, scoring two consecutive baskets to put Houston ahead by 62-58. Chambers hit one of two from the line, then the Rockets' front line of Olajuwon, Sampson and Rodney McCray each scored. All Seattle could come up with was a jumper by Ellism and the Rockets had their biggest lead of the night, 68-61, with just over five minutes remaining. Their shooting gone cold, the SuperSonics. Olajuwon scored from close in, a basket that was matched by Seattle's Kevin Williams. Sampson was fouled on the play and, with the Rockets in the bonus, made a pair of free throws. After another Seattle miss, the 7-4 center/forward scored on a hook shot to give Houston a 74-63 lead. The 16-5 stretch by the Rockets forced Seattle Coach Bernie Bickerstaff to take a timeout. The only bright spot for Seattle came with just over three minutes left, when Olajuwon picked up his fourth personal foul. Lister hit two free throws and, on Houston's subsequent possession, Sampson was whistled for his fourth foul. Chambers went to the line and hit two more foul shots. The sequence seemed to give the SuperSonics some needed energy. At the end of the quarter, Seattle had rallied back to 84-78 entering the final 12 minutes. Chambers had 14 for Seattle in the quarter; Olajuwon had eight and Sampson and McCray six each for Houston.