CHAMPAIGN, Ill. — Illinois was ahead 13-0 lead Saturday night, yet Penn State coach Ed DeChellis had a "gut feeling."

"Even the first part of the game, when they were beating us pretty good and having their way with us, I just kept telling the kids 'Just keep hanging in there, keep making some plays and maybe something good will happen,'" he said after his team upset the No. 6 Illini, 66-65, ending their 33-game home winning streak.

"We should have finished the game in the first half," said Illinois coach Bruce Weber. "We didn't have some key shutouts when we needed to."

The Nittany Lions (11-9, 3-6 Big Ten) trailed 39-25 at halftime and fell behind by 16 points twice just after the break, but they followed DeChellis' instructions and kept battling. They tied the score at 59-59 when Mike Walker dropped a 3-pointer with 4:10 to go and got their first lead of the night when Travis Parker scored what proved to be the last basket that counted with 8.5 seconds left.

Parker finished with 21 points, just one off his career high, and Geary Claxton scored 20 to lead Penn State. Jamelle Cornley added 10.

"Travis finally broke out of it. He hasn't been playing particularly well," DeChellis said, "and Claxton was a warrior all night."

Rich McBride's last-ditch 3-point shot swished and the Assembly Hall crowd erupted thinking it was a game winner. The officials huddled around a video monitor for more than a minute watching slow-motion replays and finally determined the ball left his hand a split-second too late.

"We just didn't finish the job," said Dee Brown, who was just 3-of-12 from the floor and committed five turnovers. "They came out and played the good zone and it really affected us tonight."

It was Illinois' first home loss since a 58-54 defeat by Purdue on Jan. 10, 2004. It also dropped the Illini (20-3, 6-3) out of a first-place tie with Iowa in the Big Ten standings.

"Maybe it's an attention getter," Weber said. "Maybe it will make you realize that anything can happen."

Illinois shot over Penn State's zone early. McBride dropped three 3-pointers early and that opened things up inside some in the first half as James Augustine and Shaun Pruitt helped the Illini to a 39-25 halftime lead.

But Penn State wasn't about to abandon its defense.

"We're playing zone. That's all we're playing," DeChellis said.

After Augustine's layup gave Illinois a 43-27 lead with 18:43 to go, the Nittany Lions started charging and the Illini started missing and committed some costly turnovers.

"We just got very tentative against the zone in the second half," Weber said. "I don't know if it's their adjustment or our guys not looking inside, or our guys not playing strong in there or flashing. We ran the same stuff, but obviously it wasn't as effective."

At the other end, Claxton, who played the entire second half with three fouls, was finding ways to score under the basket and Parker and Walker were pumping in shots from the outside. Parker's basket with 1:41 to go cut Illinois' lead to 65-64 and, after Illinois missed four shots in a row, he sank the game winner.

McBride led Illinois with 17 points. Augustine, who spent a significant portion of the second half on the bench with four fouls, had 13 and Brown added 11.

Illinois has a week off before traveling to No. 20 Ohio State next Sunday. Penn State plays host to Minnesota on Wednesday night.