Wins by defending champions Inter Milan and second-placed Napoli at the weekend put pressure on Milan to respond against mid-table Bologna, who were without coach Sinisa Mihajlovic on the touchline as he undergoes hospital treatment for leukemia.
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Following little improvement after the break, Milan coach Stefano Pioli called for Zlatan Ibrahimovic to come off the bench but the veteran Swede could not inspire his side to a win as Bologna withstood plenty of late pressure to seal a point.
Milan move to 67 points ahead of Napoli on 66 with seven games to play in pursuit of their first Scudetto since 2011. Third-placed Inter are three points further back having played a game less than their title rivals. Bologna stay 12th.
Milan have got results over the line in recent weeks, but their performances have not been impressive, with Pioli's side again not at their best against Bologna at San Siro.
They needed keeper Mike Maignan to keep them level with a fine save to deny Musa Barrow and, while they had 33 shots at goal, they were mostly restricted to efforts from distance with a killer chance eluding them even with Ibrahimovic on the pitch.
"We were unable to find that little moment, the twist, the shot that could change it. We did everything else," Pioli, in charge of Milan for the 100th time in Serie A, told Sky Sport Italia.
"I totally exclude the idea we felt the pressure psychologically [after wins by Inter and Napoli]. The team played with the right character, temperament and mentality, even with quality up until the final third."
Mihajlovic congratulated his Bologna squad from hospital.
"This is a difficult time for us," assistant manager Emilio De Leo said. "Mihajlovic asked us not to let go even for a moment, just as he is doing. He was proud of the performance.
"The coach spoke to the squad after the game. We had a direct video call and he congratulated the squad. The team was really pleased. We warmed his heart tonight."