Rangers stayed top of the Scottish Premier League with 81 points from 34 games but Celtic are a point behind from 33 and need only win their remaining five matches to win the league.
Samaras had the best chance of the match but saw his penalty pushed around the post by McGregor in the 82nd minute.
Scottish police said this week that parcel bombs had been sent to Celtic manager Neil Lennon and two high-profile supporters. Acrimony between Celtic, which has a predominantly Catholic fan base, and Rangers, whose supporters are mainly Protestant, is long-running and deep-seated.
Sunday's game, the seventh meeting of the teams this season, was a typically fiery encounter.
Clear-cut chances, however, were few and far between with Kyle Lafferty missing Rangers' best opening, heading wide from six metres.
Samaras got the chance to send Celtic top of the table when Steven Davis was adjudged to have blocked Anthony Stokes but McGregor guessed correctly to save his shot.
"In the second half I thought we were a far better team," Lennon told Sky Sports. "But for McGregor we would have won the game.
"I am very proud of the team today. People question our bottle but we finished the stronger team."
