It was not all smooth sailing for the Celtics, who after a 41-point first quarter found themselves two behind at the halfway stage.
The second half saw Boston keep the Pacers at a relatively safe distance for the win – which spelled serious trouble for Indiana, who were swept in the play-offs three years ago.
If Boston clean up they will likely take on top seeds Milwaukee Brewers, who are leading their best-of seven series with bottom seeds Detroit Pistons 2-0.
Oklahoma City Thunder avoided going down 3-0 to the Portland Trail Blazers with a hard-fought 120-108 win.
Russell Westbrook scored 33 points and had nearly a dozen assists, while Paul George scored 22 and Jerami Grant 18.
Damian Lillard registered 32 points for Portland, who led by a point after the first quarter but only added 17 in the second.
The Trail Blazers outstripped the Thunder on points in the third, but could not make up the shortfall by the time the game was out.
Pascal Siakam boosted the Toronto Raptors to a 2-1 play-off series lead over Orlando Magic.
The Raptors overcame the Magic 98-93 in Orlando thanks to Siakam's 30 points, 11 rebounds and four assists.
Terrence Ross scored 24 points for the Magic, while Nikola Vucevic had 22.