CHICAGO - That momentum the 76ers wanted to build heading into the playoffs?

Well, they have it. Too bad it's all going in the wrong direction.

The Sixers' 113-99 loss to the Chicago Bulls last night at the United Center was their third straight to a sub-.500 team, a turn of events that could prove disastrous given the Murderer's Row they face in the final four games of the regular season.

Beginning with tonight's hosting of the team with the best record in the NBA, the Cleveland Cavaliers, the Sixers (40-38) play three of those games - two against Cleveland, one against the defending NBA champion Boston Celtics - against two teams that are a combined 88 games over .500. And the only opponent with a losing record, the Toronto Raptors (30-48), host the Sixers at the Air Canada Centre.

All of a sudden, it's not so much a question of how high a seeding the Sixers attain for the first round of the Eastern Conference, or how many games they finish over .500. Unless coach Tony DiLeo's team rediscovers its mojo and fast, it's entirely possible the Sixers could head into the playoffs on the clipped wings of a seven-game losing streak, which would leave them at 40-42, matching last season's record.

This definitely is not what the Sixers had in mind when power forward Thaddeus Young went down on April 2 with a sprained right ankle and a bone bruise that likely will keep him out until the playoffs begin. At that point the talk was hopeful, with DiLeo suggesting that veterans Reggie Evans and Theo Ratliff and rookie Marreese Speights could hold the fort until Young returned.

So far, it hasn't happened. In fact, the fort is under siege and appears to be on fire.

"I think we really miss Thad," DiLeo said. "He is a really big part of our team. Other players have to play big minutes and he is one of our top players, so that really hurts us. The team is working on it. We are going to stay positive and stay together. At some point were are going to get Thad back."

But the Sixers weren't the only team on the floor last night missing a key player. The Bulls were without starting forward Luol Deng, who has been out since the end of February with a stress fracture in his right tibia, and backup forward Tim Thomas, the former Villanova star, who left the team to attend to a "family issue."

It took some time for everything to go wrong for the Sixers this time. Unlike Tuesday's loss at Charlotte, where the Sixers fell into a 20-point hole and staged a rally that was not sustained in the closing minutes of the fourth quarter, this was a case where they got off to a hot start and were unable to hold their lead.

Shooting guard Willie Green scored all 12 of his points in the opening period as the Sixers took a 29-22 advantage, which they expanded to 38-24 with 9 minutes, 37 seconds remaining until halftime when Samuel Dalembert tossed in a short jumper. But the Bulls, with Ben Gordon hitting back-to-back three-pointers, clawed back to make it 50-50 at intermission.

For all intents and purposes, that was the Sixers' last gasp. Although they seesawed back and forth with the Bulls (39-40) for the first few minutes of the third quarter, Tyrus Thomas sank two free throws with 6:38 left for a 63-61 lead Chicago would not relinquish.

"I really like the way we started out the game," DiLeo said. "Our defense was excellent in the first quarter. We did a good job of taking them out of things they wanted to do.

"Once they got their rhythm and momentum, it was difficult to stop them with the home crowd [the announced attendance was 20,791] getting into it. They got on a roll. Even at halftime with the tied score, I thought if we could come out and establish ourselves like we did in the first quarter, we could get control of the game. But we could not get stops."

Thomas, the third-year 6-9 forward with remarkable hops, had a career night as he matched Gordon for game-high-scoring honors with 24 points. He also was 14-for-14 from the free-throw line, a cornerstone of the Bulls' surge as they hit all 19 of their foul shots.

Contrast that with the 16-for-27 for the Sixers, which is bad enough, but worse when you consider they sank six straight in the fourth quarter after starting out 10-for-21.

As the Bulls - playing in green uniforms (to promote environmental awareness) with red trim - continued to pull away in the closing minutes, a floater by fabulous rookie guard Derrick Rose widened the gap to 105-85.

Andre Miller led the Sixers - who actually shot quite well from the field, 38-for-73 (52.1 percent), including 7-for-11 (63.6) from beyond the arc - with 20 points, while Andre Iguodala chipped in with 19 points and 10 assists, nine of which came in the first half.

"It is tough because they are getting into a rhythm at the right time," Miller said of the Bulls, who closed within 1 1/2 games of the Sixers for the sixth seed. "They are moving the ball and sharing. They are playing well off each other, taking advantage of their shooters and the fastbreak." *