MILAN, Sept 15 (Reuters) - European champions AC Milan snatched a 1-1 Serie A draw at Siena on Saturday thanks to Alessandro Nesta's injury-time strike. Milan coach Carlo Ancelotti rested Kaka among others with one eye on Tuesday's Champions League opener with Benfica but the policy backfired slightly. Visitors Milan could have scored in the first couple of minutes but were stung midway though the first half when former Middlesbrough forward Massimo Maccarone capitalised on mistakes by goalkeeper Dida and defender Kakha Kaladze to score. Ancelotti brought on striker Filippo Inzaghi for midfielder Gennaro Gattuso at halftime to boost his attacking options. Siena, who saved themselves from relegation with only five minutes to go last season, almost held on but were finally undone when defender Nesta forced the ball home. Siena's Mario Frick was then sent off for a tackle from behind as he vented his frustration at conceding so late. Milan have five points from three games, having won at Genoa on the opening weekend before drawing 1-1 at home to Fiorentina two weeks ago. Lazio host Empoli later on Saturday while leaders Juventus entertain Udinese on Sunday when AS Roma visit Reggina and injury-hit champions Inter Milan welcome Catania.