[3] Because he had three siblings, Lazar's parents would have him take a Greyhound Lines bus to the Lower Mainland for his youth ice hockey games with the Vancouver Selects.[14] The Rebels later swept the Oil Kings in the first round of WHL playoffs, but Lazar scored his first junior ice hockey goal in the elimination game, giving Edmonton their lone point in the 5–1 loss.[16] By the holiday break, Lazar had 10 goals for the season, while the Oil Kings' 11-game winning streak was broken when Jordan Weal put the Regina Pats up 6–5 with one second remaining on December 18.[18] Those seven points led the Oil Kings through their first-round sweep of the Kootenay Ice, the first time that Edmonton had won a WHL postseason series in their modern incarnation.[20] The Oil Kings then advanced to the 2012 Memorial Cup, where they were eliminated in the tiebreaker game with a 6–1 loss to the Shawinigan Cataractes of the Quebec Major Junior Hockey League.[44] At 19 years old, Lazar was the only teenager named to the Senators' 2014–15 opening-night roster, making his NHL debut on October 9, 2014,[45] for Ottawa's 3–2 loss to the Nashville Predators.[47] The Senators had the opportunity to return Lazar to the Oil Kings within 10 games of his debut without burning a year of his entry-level contract, but coach Paul MacLean was impressed by his early performance and chose to retain him beyond that point.[50] While the Senators lost their opening-round series in the 2015 Stanley Cup playoffs to the Montreal Canadiens, the third line, in which Lazar played with Jean-Gabriel Pageau and Erik Condra, showed promise for future seasons.[53] Despite his versatility, Lazar had difficulty scoring in his sophomore season: by the end of November, he had only two goals, one of which came on an empty net, and he began watching videos of himself with the Oil Kings to isolate his troubles.[58] After scoring three goals in 13 AHL games, Lazar was promoted back to Ottawa on November 19, helping the team through injuries to Hoffman, Bobby Ryan, and Clarke MacArthur.Additionally, the acquisitions of veteran forwards Alex Burrows and Viktor Stålberg gave Lazar little opportunity to play as the season progressed, and he was a healthy scratch for five of his last nine games with Ottawa.[65] With the Flames facing elimination by the Anaheim Ducks in the first round of 2017 Stanley Cup playoffs, Lazar and Freddie Hamilton drew into the lineup in place of Matt Stajan and Lance Bouma.[69] Playing as a fourth-line grinder gave Lazar a steadier role within the Flames: despite having only two goals and five assists through 51 games, he received far fewer healthy scratches in the second half of the season.[76] He spent most of the call-up as a healthy scratch and was sent back down three weeks later, but a series of illnesses and injuries in mid-March created another promotion opportunity for Lazar.