The 1-1 result saw Milan drop three points behind league leaders Juventus with five games remaining.
Milan have won just one of their last four league games but are still in second place ahead of Wednesday's home game against strugglers Genoa.
Allegri said: "Our last performances have not been up to standard.
"We have made many mistakes and we are not as sharp as we were a month ago but this should not be an excuse to not win certain games.
"My players and I believe it is possible to win the league title because we are just three points behind Juventus and in football anything can happen.
"Our aim remains the same, to try to win the scudetto."
Rivals Genoa endured a turbulent weekend and newly appointed coach Luigi De Canio will be looking to get his side's season on track.
Alberto Malesani was sacked following Sunday's 4-1 defeat to Siena which extended the Grifoni's winless run to 12 games.
That dismal run has seen them fall into 17th place, just one point clear of the relegation zone.
Sunday's game was marred by unruly behaviour by a section of Genoa fans, which led to the encounter being stopped for 45 minutes before the game continued.
The Italian league have ordered Genoa to play its final two home games of the season behind closed doors.
Should De Canio fail to stop his side's freefall, Genoa could find themselves in the bottom three on Wednesday night.
De Canio feels it is only a matter of time before his side stop the rot.
"Tomorrow's [Wednesday's] game is important," he said. "No rival gives away anything.
"My team has not won a game in a long time but it has to find the strength to change this trend immediately."
Allegri welcomes back defender Thiago Silva and midfielder Kevin Prince Boateng from injury while defender Daniele Bonera must serve a one-match ban.
The visitors will be without defender Giandomenico Mesto and midfielder Marco Rossi, both suspended.