The Portuguese outfit were already three points clear of second-placed Besiktas heading into the match and hoping to seal their progress after three wins from three.
- FC Porto 1-1 Besiktas: As it happened
However, Nihat Kahveci's second-half equaliser after Radamel Falcao Garcia's penalty ensured the Turkish side escaped with a point after a second half which saw both sides reduced to 10 men.
The key man in the early exchanges was Hulk, the Brazilian forcing Hakan Arikan into action with a 30-yard free-kick which the goalkeeper caught.
Hulk had another shot blocked before setting up Falcao for a volley which went over the bar.
Alvaro Pereira crossed for Falcao but again the striker shot over the top.
Besiktas were barely in the game as Hulk forced another save from Arikan and Falcao smashed a third attempt over the bar.
Nihat forced a save out of Helton before Guti sent a shot wide following another decent move.
In the 35th minute Porto were ahead, however. Arikan rushed out and brought down Falcao and from the resulting penalty, the Colombian gave the home side the lead.
Cristian Rodriguez picked up his first booking for handball before the half was out and Rodrigo Tabata had a chance which was off target.
The second half had an uneventful start punctuated only by a Hulk shot in the 57th minute. The powerful striker made room for himself before blasting the ball from around 12 yards only to see Arikan make a sprawling save.
Things livened up in the 59th minute when a spat between Rodriguez and Ibrahim Uzulmez saw both players booked - crucially, Rodriguez for the second time and he was shown the red.
Two minutes later Besiktas were level, Nihat picking the ball up from deep and launching a 30-yard rocket which left Helton with no chance.
The numbers were evened up by the 66th-minute dismissal of Ibrahim Toraman for a second booking.
Bobo fired one over the bar for Besiktas in the 70th minute and came even closer four minutes later when he smashed a volley against the bar from all of 35 yards, before Porto's Ruben Micael produced a similar attempt but was too high.