Gennaro Gattuso had given the visitors a 16th-minute lead but Antonio Langella equalised before half-time.

Tissone then put Atalanta in front on 68 minutes to end his team's five-match winless run.

Milan had been hoping to reduce the gap on the top four in Serie A, but the result leaves them 10 points behind Fiorentina, who hold the last Champions League qualifying spot, although the Rossoneri still have two games in hand.

AC Milan coach Carlo Ancelotti fielded Alberto Gilardino and Alexandre Pato in attack, leaving Ronaldo on the bench.

Gilardino had come off the bench to score the only goal at Udinese last Sunday but this time he was unable to come up with the goods.

Atalanta enjoyed the first chance of the game with Tissone's cross finding Cristiano Doni inside the area, but his effort went high over the crossbar.

Milan put some good moves together but struggled to find the finishing touch until Gattuso broke the deadlock on 16 minutes.

His powerful right-footed strike took a deflection off Doni before beating goalkeeper Ferdinand Coppola.

The goal inspired the Rossoneri, who should have doubled their lead midway through the first half.

Gilardino latched onto Kaka's cross but his header went wide of the far post.

On the half-hour mark, Clarence Seedorf lobbed the ball beyond Coppola but saw his effort flash wide of the post.

Pato then missed a golden chance to make it 2-0 after a defensive mistake by the Atalanta defence left the Brazilian youngster with only Coppola to beat, but his close-range effort went wide.

Milan's lack of precision cost them dearly as Atalanta equalised on 42 minutes.

Langella got past two defenders before firing a right-footed strike past Milan goalkeeper Zeljko Kalac.

Shortly after the interval, Seedorf tried his luck from distance and his effort went high over the bar.

At the other end, Langella put a great cross in towards Doni who just failed to make contact with the ball eight yards out.

Ancelotti made his first substitution shortly after the hour mark with Ronaldo replacing Pato.

Coppola then did well to anticipate Ronaldo inside the area, who was ready to fire from Gattuso's cross.

But Milan were hit by another goal soon after.

Substitute Simone Inzaghi's assist served Tissone who made no mistake from point-blank range.

Kalac was forced to dive to his right to clear Inzaghi's angled strike while seconds later, Morris Carrozieri's free-kick went just wide of the far post.

Ronaldo then surged inside Atalanta's area but his effort was met by a fine save from Coppola.

But it was the hosts who came closest to finding the back of the net with Tissone's strike beating Kalac but rebounding off the crossbar.

Milan twice had the chance to equalise before the final whistle but Coppola pulled off two great saves to keep out Kaka's right-footed effort and Seedorf's bullet-strike.