He then folded the white towel in half, a good sign for Cavaliers fans. He wasn't waving it in surrender.
The Cavaliers braced for the worst and received it with an MRI exam Friday: Irving will need three to four months of recovery after surgery within a few days, the team said.
Irving left Game 1 of the NBA Finals in overtime, crumpling to the court while driving toward the basket in the Cavaliers' 108-100 loss Thursday to Golden State.
Losing the All-Star point guard is a decisive blow for Cleveland, trying to capture its first NBA championship in 45 years of existence.
Irving, 23, has been bothered by soreness in the knee in recent weeks and missed two games of the Eastern Conference finals because of what the team called severe tendinitis.
Before news of Irving's injury was disclosed, James tried to sound as upbeat as possible. Irving averaged 19 points and 3.8 assists in the playoffs.
"The good thing about it, we've been in this position before," James said. "If he's not able to go, it's something that's not new to us. So, next man up, and guys will be ready for the challenge."
Unfortunately for the Cavaliers, few were up for the challenge in Game 1 besides James (44 points), Irving (23 points, six assists) and Timofey Mozgov (16 points).
The reserves totaled nine points, all of them coming from cold-shooting J.R. Smith (three for 13).
The pressure now will be unimaginably heavy on James, who tried to make good with the city of Cleveland by returning there after four years with the Miami Heat.
He has been stellar in the playoffs, averaging 28.7 points, 10.3 rebounds and 8.1 assists, but this now feels like a monumental mission. Except maybe to James.
"There are a few things that you would love to have going late in the season — being healthy, having a great rhythm, and then you need a little luck as well. We've had a great rhythm, we haven't had much luck and we haven't been healthy," he said. "But I haven't gotten discouraged. I'm excited to be in this moment once again, and I'm going to stay strong for my team, no matter who is or is not in the lineup."
He'll have to do it with an unremarkable supporting cast starting to look like his teammates in 2007, when the Cavaliers and a 22-year-old James were swept by San Antonio.
Second-year guard Matthew Dellavedova averaged 14 points and three assists while starting two games in Irving's absence in the East finals. He figures to get the call again, but plenty of work will fall upon Smith and Iman Shumpert, role players acquired by Cleveland in a midseason deal with New York.
Smith can be gifted on offense but also prone to erratic play. He averaged 18 points and four three-pointers per game in the East finals against Atlanta, following it up unsuccessfully in 34 minutes of Game 1 in the Finals.
Shumpert averaged 15.5 points in the two games Irving missed but usually isn't much of a scorer. He was a combined two for 15 in the other two games of the East finals and had only six points Thursday.
The Warriors were the favorites before the Finals started and now appear much more so.
They absorbed a great road effort in the opener by Cleveland and won when the Cavaliers went dry in overtime, scoring only two points. In Game 2, the deep Warriors again plan to use 10 players.
Reserve forward Andre Iguodala had an unexpected 15 points on offense and often defended James by himself. The Warriors were conceding the fact James could score at will (he had 44 points) while trying to take away his passing.
It was unclear if that would be the Warriors' Game 2 strategy, but there were many smiles from them Friday, sensibly enough, Stephen Curry showing no letup at all while averaging 30.3 points and six assists over his last six games.
He had fun with a reporter who pointed out Curry had made 12 consecutive three-point attempts from the left corner.
"You jinxed me already. That's a death wish for Game 2," Curry said with a laugh. "I need to know where you're sitting at in Game 2. I'll point at you if I miss it."
The Warriors could afford some fun. Forty years since their last championship, everything looks increasingly promising for them.