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Michael Perez, Associated Press
Chicago Bulls' Taj Gibson (22) stares at an official after a foul called against him during the second half of Game 4 in a first-round NBA basketball playoff series against the Philadelphia 76ers in Philadelphia, Sunday, May 6, 2012. The 76ers won 89-82.

DEERFIELD, Ill. — It seemed almost unthinkable that the Chicago Bulls could be in this spot.

Yet here they are, trailing the Philadelphia 76ers 3-1 in the first round and trying to avoid elimination as they return home for Game 5 on Tuesday night.

If the Bulls lose, they will be just the fifth No. 1 seed to fall to an eighth seed. It would also give Philadelphia its first series victory since 2003, a scenario few envisioned when the postseason started.

"It's been a crazy year from beginning to right now," guard Richard Hamilton said Monday. "We know that."

They also realize it'll take a wild comeback for them to advance, particularly given their injuries. They lost Derrick Rose for the remainder of the season to a torn anterior cruciate ligament in his left knee late in the series opener, and center Joakim Noah will likely sit out his second straight game because of a sprained left ankle, leaving them without two of their leaders.

As they staggered back home following Sunday's 89-82 loss, they sure looked like a beaten team. History says they're just about finished, too. Only eight teams have come back from a 3-1 deficit to win a best-of-7 series.

Hamilton wasn't conceding anything. He was with Detroit when the Pistons turned the trick in 2003, beating in the first round Orlando after falling behind 3-1 and advancing all the way to the conference finals.

"When we played Orlando, I remember Tracy (McGrady) made a comment saying that it feels good to be going to the second round, so we kind of took that personally," Hamilton said. "Right now, it's personal. It's not just about business. ... It's personal. This is it. You can win and continue playing, or you can go home, so you've got to make it personal."

The 76ers weren't making any bold statements after Game 4, even though they're on the verge of a rare feat. The only other eight seeds to knock off a No. 1 are Denver (1994), New York (1999), Golden State (2007) and Memphis last season, when it eliminated San Antonio, but while they put themselves in a good spot, they also got a few words of caution from associate head coach Michael Curry.

Like Hamilton, he played on that 2003 Pistons team.

"I think Michael Curry was great in the locker room yesterday when he talked about the Detroit-Orlando situation," coach Doug Collins said. "You can't go in with the idea we've got three games to win one. That would be very bad psychology. We've got to go in with the idea that we want to go to Chicago and we want to finish the series."

Andre Iguodala agreed.

"We're hungry and we still want it just as bad as if we were down 0-3," he said. "We've got to come in and play like this could be our last game."

For Chicago, it has simply been a brutal series.

Rose was looking more like an MVP after missing 27 games during the regular season because of injuries when he went down late in Game 1, and the Bulls haven't been the same without their superstar.

They got plowed over in the second half while dropping Game 2, and things only got worse in Game 3. As if watching their best player go down weren't enough, they lost one of their emotional leaders after Noah stepped on Iguodala's foot while driving the lane.

And in Game 4, they again came up short.

Jrue Holiday has been giving them fits, averaging 19.8 points in the series. He nailed two 3-pointers down the stretch on Sunday after struggling most of the game. Spencer Hawes has been a big headache, too, shooting over 57 percent and averaging 12.5 points in the series.

The Bulls, meanwhile, have gotten little from Luol Deng. Carlos Boozer has been inconsistent, and Hamilton can't even get on the court down the stretch, with coach Tom Thibodeau going with Kyle Korver instead. He sat out the entire final period in each of the first two games and was in for just 27 seconds in Game 4 after playing 9 minutes, 43 seconds in the fourth quarter of Game 3.

"You do (want to play in the fourth), but it is what it is," Hamilton said. "Whatever they need me to do, I'm going to do. My job is if I'm not on the court in the fourth quarter is to cheer for the next guy because I know the next guy would do the same thing for me."

The Bulls came in with big expectations, eyeing a possible rematch with Miami in the Eastern Conference finals after grabbing the No. 1 overall seed for the second straight year.

Now, they're in a spot few envisioned.

"That's where your mental toughness, your physical toughness come into play," Thibodeau said. "Hopefully, you've been building the right habits all season long to get through situations like this. Every team in the playoffs is going through the same thing. There's going to be ups and downs. You have to be resilient. You have to persevere. You have to get through things.

"But we have more than enough to win with," he continued. "We just have to finish it off."