Tempers flared after the final whistle when Porto coach Julen Lopetegui crossed paths with his Benfica counterpart Jorge Jesus, who had to be pulled away by his staff after the pair began arguing.
"It's not normal for that to happen, it was the adrenaline," Jesus, who had shaken hands with Lopetegui before the game, told reporters.
With only four matches left in the 34-match campaign, the draw at Benfica's Estadio da Luz leaves the champions on 75 points, still three points clear of their old foes.
Remarkably, it was the first time for six years that Benfica had failed to score in a home league match since a 1-0 home defeat to Academica Coimbra in April 2009.
Leaders Benfica were happy to let their nearest pursuers take the initiative on their home turf but Porto, eliminated from the Champions League on Tuesday with a humiliating 6-1 defeat at Bayern Munich, could not find a way past veteran Brazilian goalkeeper Julio Cesar.
With both starting line-ups featuring six Brazilians, Porto had the only real chance of the first half when striker Jackson Martinez, the championship's top scorer with 17 goals, fired over from near the penalty spot.
Benfica had to wait until five minutes into the second half for their first shot on goal but Anderson Talisca's effort was comfortably stopped by Helton.
Martinez came close again for Porto before Serbian substitute Ljubomir Fejsa missed a late chance to win the game for Benfica when he fired over from close range.
"We deserved to win the game. They were wasting time near the end and their goalkeeper was booked for it," said Lopetegui.
"One team tried to attack and the other to defend. We showed great personality to come back after our game in midweek."
Third-placed Sporting Lisbon, now nine points behind Porto, will attempt to close the yawning gap on Monday at Moreirense.
(Writing by Brian Homewood in Berne; Editing by Ian Chadband)
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