Trailing their best-of-7 playoff series with the Lightning 2-1, the Bruins think some extra effort is called for in Game 4 on Friday night at TD Garden.

Mike Loftus The Patriot Ledger

 BOSTON -- They don’t have to worry about a third strike retiring them.

 There’s a lot to be said, however, for evening the count, and if the Bruins don’t do that in Game 4 of their best-of-seven playoff series against the Lightning on Friday night at TD Garden (7:05, NBCSN, WBZ-FM/98.5), their second-round appearance isn’t likely to last much longer.

“You’re getting to the point now where you need to win,” said coach Bruce Cassidy, whose team has dropped two in a row since he warned after a 6-2, Game 1 win at Tampa that some areas of its game had to improve.

“We need to win at home. We didn’t let (Game 3, a 4-1 loss) get away, but we didn’t take advantage of what we did on the road, so we have to (win on Friday).”

The Bruins are battling multiple issues entering Game 4. Scoring has dried up (three goals since Game 1) because they’ve so rarely been in possession of the puck, and when they have had it, they’ve made too many mistakes with it. Unforced turnovers gave the Lightning two outmanned rushes that became goals in the Bruins’ 4-2 loss in Game 2.

Compounding the puck-possession problems: The B’s aren’t defending well. Two of the Lightning’s three first-period goals in Game 3 were byproducts of weak coverage in the Bruins’ defensive zone.

Which matter to address first? Neither. The Bruins believe working harder than they did in the last two games will straight them out, and tie the series up.

“Obviously, in the playoffs, you need to be willing to outwork the opposition,” captain Zdeno Chara said. “That hasn’t been the case in the last two games.”

“I think in the last two games, at certain points, more than at any time during the year, we got outworked a little bit,” said rookie center Sean Kuraly. “I don’t think it was anything intentional on our part, obviously, but I think we just want to raise our compete, and win battles. Then we think things will go our way.”

Extra effort must be wide-ranging and can’t be sporadic, because the Lightning has used multiple ingredients to pull ahead. Tampa Bay, which beat out the B’s for first place in the Eastern Conference by a single point, has shown enough offensive depth to survive without a meaningful goal from its top line of J.T. Miller, Steven Stamkos and Nikita Kucherov (the trio figured in its first goal in Game 3 -- an empty-net power-play goal with 42 seconds remaining), as well as impressive ability to protect and play with a lead.

Compelling examples of both qualities came in Game 3 on Wednesday. Less than three minutes after Patrice Bergeron’s power-play goal pulled the B’s within 2-1, the Lightning’s third line of rookie Anthony Cirelli (first career playoff goal), Yanni Gourde and Alex Killoran bumped the lead back to two goals with 3:17 left in the first period; the Lightning then limited the Bruins to 15 shots at goalie Andrei Vasilevskiy over the final 40 minutes.

“There’s a reason why they’re the first-place team in the East,” B’s winger Rick Nash said. “They know how to win games.”

Cassidy ran the Bruins through a 30-minute practice on Thursday, the focus primarily on improving defensive zone coverage, and using it to break pucks out quickly and cleanly. The coach probably won’t stop there, either: Forced on Friday to change some line combinations because left wings Brad Marchand and Jake DeBrusk were given maintenance days, Cassidy indicated he’d probably make changes by choice in Game 4.

“We’ll probably tinker,” the coach said. “I’m not going to tell you who’s going in and who’s going out now. We’ve got to get the healthy guys sorted out first, and then go from there.”

Whether Cassidy chooses to add Scituate’s Ryan Donato to the lineup for just the second time this postseason, or make a smaller move like restoring fourth-line winger/penalty-killer Tim Schaller after scratching him for the first time all season in Game 1, everyone in uniform must be prepared to work from the start.

“Drop of the puck, we need to be ready -- focused, in sync, engaged, urgent -- to make sure we’re not giving anything for free,” said veteran winger David Backes. “In playoffs, anything for free is a hole you’ve dug yourself, and it’s tough to dig out of.”