Matthews said later that he first thought someone had hit him from behind. It was far worse.
A key contributor on the floor and in the locker room, Matthews ruptured his Achilles tendon. He missed the final 22 games of the regular season, and the Blazers finished that stretch 10-12.
Matthews' absence, along with other key injuries, had both the team and its fans wondering what might have been following Portland's first-round playoff loss to the Memphis Grizzlies in five games.
''It is all bittersweet because this season was a battle for us. Having 50 wins is always a good season, being division champs is always good but we definitely did not want to lose like this,'' LaMarcus Aldridge said.
The previous season, when the Blazers stayed healthy all season long, they advanced to the second round for the first time in 14 years. Early this season, with core starters Aldridge, Matthews, Nicolas Batum, Robin Lopez and Damian Lillard all healthy, the Blazers went 24-8. But injuries took a toll.
Lopez was the first casualty, missing 23 games with a broken right hand. Then Aldridge tore ligaments in his thumb in late January, but ultimately decided to play out the rest of the season and manage the pain. Nicolas Batum battled a nagging wrist injury.
The only player to start every game this season was Damian Lillard. Portland nevertheless finished 51-31 and claimed the Northwest Division title.
It may well be the last time that core group is together will turn out to be that game against the Mavericks back on March 5. The Blazers' roster includes nine free agents, including Aldridge, Lopez and Matthews.
Aldridge, a four-time All-Star, has played each of his nine NBA seasons in Portland after the team acquired him with a draft-night trade in 2006.
At the season's start, he said he planned to re-sign with the Blazers during the free agency period. Blazers general manager Neil Olshey and team owner Paul Allen personally met with Aldridge and his agent last summer to pledge the team's commitment to him.
He averaged 23.4 points and 10.2 rebounds during the regular season. In the playoffs, he averaged 21.8 points and 11.2 rebounds, but shot just 33 percent from the floor doing battle with Memphis' Zach Randolph.
Aldridge was noncommittal on Thursday, although he proclaimed his affection for Portland. He said he'll speak to his family and his agent about his decision, and that he would prefer not to drag out the process.
He'll also look into whether surgery is still necessary on his thumb.
''As of now, I'm about to relax,'' he said. ''My body's beat up.''
While the offseason was uncertain for the team as a whole, the Blazers did see dramatic progress in two players in particular: Meyers Leonard and CJ McCollum.
In Game 5 against Memphis, McCollum had a career-high 33 points and made seven of his 11 3-point attempts. He was instrumental in erasing a 13-point deficit with 16 points in the third quarter.
The second-year guard was thrust into an increased roll when Arron Afflalo - who was acquired at the trade deadline from Denver and did his best to replace Matthews - injured his right shoulder at the end of the regular season.
Leonard, a 7-footer who fought for minutes behind Lopez and Chris Kaman, found a niche as a perimeter shooter, and made 10 of 13 in the series against the Grizzlies.
''We had pretty high expectations for this year, but now that it is over you figure out what you can do for next year, how you can get better individually, and as a team,'' Leonard said. ''I am pretty pumped for the offseason.''
Leonard, McCollum, Lillard and Batum are the only players on the roster with guaranteed contracts next season.
''I don't know what's going to happen next,'' Batum said. ''I hope we have the same guys next year.''