Porto's 2-1 defeat at Famalicao on Wednesday gave Benfica the opportunity to go two points clear at the summit but, despite dominating the match at an empty Estadio da Luz and having 24 shots at goal, they failed to find a way through.
The draw took Benfica back to the top on goal difference although they are locked on 60 points with Porto after 25 games. Tondela are 13th with 26 points, seven above the drop zone.
Benfica defender Ruben Dias headed against the woodwork from a corner in the second half while substitute Dyego Sousa also headed against the frame of the goal and then had a shot cleared off the line in added time.
"We were almost always in the opponents' half, we created a lot more opportunities, we were the best team on the pitch, we played pretty well but that is not enough," said Benfica coach Bruno Lage.
"It is a shame we did not take this opportunity to make a good start and go clear at the top of the championship."
With no fans allowed at the match to prevent the further spread of the novel coronavirus, Benfica scarves were hung on the empty seats in an attempt to bring some colour to the bare 60,000 capacity stadium.
"The presence and warmth of the supporters was missing. It was yet another element that was missing today," added Lage.
Benfica's neighbours Sporting played out an entertaining 2-2 draw at Vitoria Guimaraes, twice taking the lead through Slovenian striker Andraz Sporar but Joao Carlos Teixeira and then Marcus Edwards levelled for the home side.
Sporting also failed to take advantage of Joseph Amoah being sent off for the home side in the 77th minute and the draw leaves them fourth on 43 points, while Vitoria are sixth on 38.