TORONTO -- Star center Auston Matthews did not finish Saturday night's Game 4 because of an illness, as the Toronto Maple Leafs fell 3-1 to the Boston Bruins.

Toronto now finds itself on the brink of elimination in its first-round playoff series, with a must-win Game 5 on Tuesday in Boston.

Coach Sheldon Keefe previously confirmed Matthews played through an illness in Game 3, and Matthews had been absent from multiple team sessions while recovering. It was more of the same in Game 4 when Matthews logged 14:16 in ice time before not returning after the second intermission.

"It is all related to the illness he's dealing with," Keefe said, responding to a reporter's question on why Matthews didn't return for the third period. "The doctors pulled him."

Matthews was Toronto's hero in Game 2, scoring the game-winning goal and notching two assists to lift the Maple Leafs to a 3-2 victory.

It was the Bruins again taking it to Toronto early Saturday. Boston jumped out to a 1-0 lead off James van Riemsdyk's opening goal to enter the second period ahead 1-0, and it quickly added to its lead with a power-play goal from Brad Marchand. David Pastrnak collected another with 41 seconds left in the middle frame to afford Boston a 3-0 advantage going into the third.

Toronto has now lost six straight playoff games at home, a streak dating to the 1970s, and has been outscored 21-11 in that stretch of home contests. The Leafs have also scored three or fewer goals in 11 consecutive postseason tilts to date.

Emotions were visibly boiling over for Toronto on the bench in Saturday's loss, with cameras capturing Matthews, Mitch Marner and William Nylander -- back in the lineup after missing the series' first three games with an undisclosed injury -- exchanging verbal barbs.

"We're grown men," Marner said of their exchange. "We're just talking about plays out there that we all want to make sure we're 100% on. Just a little off page there. We're not yelling at each other because we hate each other. We just all want to be on the same page and help each other out."

Marner was the lone goal scorer for Toronto when he broke through with his first of the playoffs to cut Boston's lead to 3-1 in the third period. That was all Toronto could muster, though, offensively. The Leafs' power play continued to misfire and finished 0-for-3 in Game 4, to put them 1-for-14 on the man advantage in the series to date. Meanwhile, Boston has capitalized on its special teams' opportunities with another power-play goal on Saturday (6-for-13 in the playoffs).

The gravity of Toronto's situation now isn't lost on anyone.

"We're down 3-1," Nylander said. "It's not a great spot to be in."

Keefe opted to make a goaltender change for the final frame by inserting Joseph Woll for Ilya Samsonov, who had allowed three goals on 16 shots (.813 save percentage). The Leafs' coach declined to name a starter for Game 5.

"The reason for [the swap] is we're just trying to change things," Keefe said. "You get to get Joe involved. That's really it. You're trying to change the momentum. We've got some time here to talk it through [before Game 5]."

Boston went back to Jeremy Swayman in its net to break the goalie rotation it had cultivated between him and Linus Ullmark. Swayman had led Boston to victory in Game 1 and Game 3; Ullmark started the Bruins' lone losing effort in Game 2. Coach Jim Montgomery explained on Saturday the plan had been to give each of Swayman and Ullmark a postseason start and then decide on a regular goaltender from there. Given Swayman's success, it was an easy choice for Montgomery to keep him in the crease.

Montgomery had previously questioned if Swayman was "in [the Maple Leafs'] heads," given his success against them all season. Swayman is now 6-0-0 against Toronto and holds a .956 save percentage through three postseason games.

Keefe felt it wasn't for lack of trying that Toronto hadn't been able to crack Swayman.

"I don't sense any frustration," he said. "Guys are pushing one another, guys are competitive, guys want to win. It's all part of it."

Toronto can only turn the page now to Game 5 on Tuesday, where the Leafs will extend -- or end -- their season.

"There was nothing wrong with our effort level here tonight," Keefe said. "Guys are competing. It's physical hockey. Guys are trying. That's a good team over there. It's limiting us. You can question a lot of things, can't question the effort."