Primer: The blockbuster 2014 trade deadline deal between the Lightning and Rangers that saw Ryan Callahan and Martin St. Louis swap teams could prove relevant in deciding the Eastern Conference finals one year later. But both players, who have yet to score in the playoffs, must break out of slumps first.

Callahan, who spent his first five NHL seasons with the Rangers, has three assists in 12 games but is a plus-7. He’s coming off an emergency appendectomy on Monday that kept him out of the Lightning’s Game 6 win over the Canadiens. After eight goals and 15 points in last year’s playoffs, St. Louis has four assists in 12 games. He spent 12 seasons in Tampa before the trade and was a big part of the Lightning’s only Stanley Cup win in 2004.

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All of the Rangers’ games this postseason have been decided by one goal, part of an NHL record streak that extends to last season’s playoffs. 

Dates and times (all times Eastern; * — if necessary): 

May 16: Rangers 2, Lightning 1Monday, May 18: at Rangers, 8 p.m.; NBCSN, CBC, TVAWednesday, May 20: at Lightning, 8 p.m.; NBCSN, CBC, TVAFriday, May 22: at Lightning, 8 p.m.; NBCSN, CBC, TVASunday, May 24: at Rangers, 8 p.m.; NBCSN, CBC, TVATuesday, May 26: at Lightning, 8 p.m.; NBCSN, CBC, TVA*Friday, May 29: at Rangers, 8 p.m.; NBCSN, CBC, TVA

Regular-season series: Lightning won 3-0

How they got here: The Rangers made easy work of the Penguins in five games, and then outlasted the Capitals in seven. The Lightning beat the Red Wings in seven games before sending the Canadiens home in six.

Injuries: Callahan resumed skating Thursday morning and is expected to be ready to play in Game 1.

Rangers defenseman Dan Boyle was knocked out of their Game 7 win against the Capitals when he took a nasty hit above the shoulders from Brooks Orpik. Rangers coach Alain Vigneault seemed optimistic about Boyle’s return, telling WFAN on Thursday that Boyle “feels a lot better."

The Rangers could also be without forward Mats Zuccarello, at least for the start of the series. Zuccarello hasn’t played since Game 5 of the first round with what is believed to be a concussion. Vigneault said Thursday that Zuccarello was working out on his own and is keeping his “fingers crossed” for a return in the series. 

Key players: This series’ two biggest stars, Steven Stamkos of the Lightning and Rick Nash of the Rangers, both have gone through rough patches in this postseason. Stamkos went the first eight games without a goal but has seven points in his past five, including three goals. Nash started out strong but has three points in his past eight games. He’s tied for 25th among playoff scorers with seven points in 12 games.

The Rangers’ leading scorers are Derick Brassard and Derek Stepan with eight points apiece. The Lightning have four players with eight or more points: Stamkos, Ondrej Palat, Alex Killorn and Tyler Johnson, whose eight goals lead the playoffs.

Goalie matchup: This series could well be decided in net as two of the playoffs’ hottest goaltenders go head to head. Henrik Lundqvist of the Rangers leads all goalies (with five or more starts) in goals-against average (1.60) and save percentage (.944) and is the hands-down favorite to capture the Conn Smythe Trophy should the Rangers go the distance. His counterpart, Ben Bishop, is third among goalies with a 1.81 GAA and .931 save percentage. Bishop has been a rock for the Lightning in the first playoff hockey of his career.

Prediction: Rangers in six.