TAMPA — It's easy to point to the elite talent on the Lightning's roster when looking for a reason as to why the Lightning is once again among the NHL's best teams again this year.Tampa Bay has one of the NHL's point leaders in Nikita Kucherov. It has one of the league's top goal scorers in Brayden Point. It has two top defensemen in Victor Hedman and Ryan McDonagh.But it's the depth that makes this Lightning team truly dangerous. It's the depth that has this team in contention for a Stanley Cup once again. And it's the depth that sparked the Lightning late against the Bruins.Third and fourth liners in Mathieu Joseph and Anthony Cirelli scored two third-period goals to give Tampa Bay a 3-2 victory over Boston at Amalie Arena. The Lightning (22-7-1) remains atop the NHL with 45 points."It's hard to play against a team with four lines rolling like this," Joseph said. "I think every line can play any line. We're a team that has a lot of depth. It's huge. I think that's why he has so much confidence in all the lines. It definitely brings a lot to the table during games."Part of the confidence stems from the ability to mix and match lines with a fair amount of ease. One moment, a player could be on the fourth line and the next game, he could find himself on the first line. Or, he could play on the fourth line one period and the third the next.That's what Joseph did Thursday.After playing on the fourth line for the first two periods, Lightning coach Jon Cooper moved him to the third line. Three minutes into the period, Joseph scored to give the Lightning a 2-1 lead."If you miss one or there are different lines out, it doesn't really matter as much for me as a coach," Cooper said. "I have a lot of confidence as a coach. And they have definitely delivered."Cirelli added his goal about 90 seconds later, which came during a Boston power play. Lightning captain Steven Stamkos set up Cirelli's breakaway as he batted the puck while falling to the ground. Stamkos had lost his stick. The batted puck ricocheted off a defender to Cirelli.It was Cirelli's fifth goal of the season. Joseph, a rookie, tallied his ninth of the season.Fourth-line center Cedric Paquette didn't get in on the scoring Thursday, but he has also been key for the Lightning on this five-game winning streak. He scored the game-tying goal late against Detroit and scored the game-winner against Buffalo that snapped the Sabres' 10-game win streak. His seven-goal total has already eclipsed his scoring for the past three seasons."(Depth) has been one of our strengths, especially last year in the playoffs against Boston when all four lines were rolling," Goaltender Louis Domingue said. "Our fourth line was one of our best lines in the playoffs. It's definitely the strength of our team."But it doesn't hurt for the Lightning to have elite players such as Point. He proved as much in the first period.Two minutes into the game, Domingue denied the first shot he faced from Colby Cave, but David Pastrnak kicked the rebound to himself and dove to give the Bruins a 1-0 lead with 17:56 left in the first period.Before the first period ended, Point responded. With 5:01 left in the first, Nikita Kucherov hit Point with a backhanded pass, and Point turned that pass into his 21st goal of the season to tie the game at 1-1.It's the combination of elite talent such as Point and Kucherov combined with quality depth in players such as Cirelli and Joseph that has this Lightning team at the top of the league and a team that should make another deep run into the postseason."Depth is key," Cooper said. "There's no question. Your big players get a lot of minutes. They play special teams. They do all these things, but somebody has to be able to fill the gap there. You've got to be able to play the game different ways. That's what I feel we have been pretty good at."