Adjust font size:
ROME, Italy -- Ronaldo scored two goals and set up another as AC Milan beat Siena 4-3 to climb to fifth in Serie A on Saturday.
Milan only claimed victory in the final minute of stoppage time when Massimo Ambrosini headed in from a corner but the dominant figure was three-times FIFA World Player of the Year Ronaldo, making his first appearance in Milan's starting line-up since signing from Real Madrid last month.
Milan have 33 points after 23 matches, taking into account their eight-point penalty for match-fixing, and are 30 points behind leaders Inter Milan, who racked up their 16th successive Serie A win by beating Cagliari 1-0.
Second-placed AS Roma slipped 14 points behind Inter after losing 1-0 at Empoli.
Ronaldo inspired Milan to a dramatic victory after Siena had pulled themselves level each time they fell behind, only to succumb to Ambrosini's header in the final seconds.
The Brazilian opened the scoring in the 15th minute, out-jumping his marker to nod a Paolo Maldini cross past keeper Alex Manninger.
Midfielder Simone Vergassola equalized four minutes later but Ronaldo conjured up a defense-splitting pass for strike partner Ricardo Oliveira to restore Milan's lead just before the half hour.
Siena levelled again, January signing Massimo Maccarone pulling down a cross before angling a shot past goalkeeper Marco Storari.
Milan's chances of victory dipped in the 77th minute, when midfielder Cristian Brocchi was sent off for a clumsy challenge on Francesco Cozza.
But three minutes later Ronaldo struck again, tapping in from close range after a superb solo run and cutback by playmaker Kaka.
Maccarone seemed to have grabbed a point for Siena when he was left unmarked at the far post to fire in his second goal two minutes from the end.
Milan made it six victories in their last seven Serie A matches, however, thanks to Ambrosini's last-gasp winner.
Inter's victory at the San Siro stadium was a more prosaic affair. Defender Nicolas Burdisso headed the winner from a Zlatan Ibrahimovic cross in the 11th minute.
The leaders went close again when Dejan Stankovic thumped a shot off the crossbar 10 minutes from the end.
Roma's performance in their defeat to fourth-placed Empoli (35 points) will have failed to impress Olympique Lyon coach Gerard Houllier, watching from the stands at Empoli's Castellani stadium.
Roma host Lyon in the Champions League on Wednesday.
The game was settled by a fifth-minute goal from Empoli striker Nicola Pozzi. Roma's David Pizarro and Simone Perrotta hit the post in the first half.
Hat-trick for Del Piero
Alessandro Del Piero scored a hat-trick as Juventus routed Crotone 5-0 to go three points clear at the top of Italy's Serie B.
The win gave Juventus 43 points after 23 matches, taking into account a nine-point penalty imposed as punishment for its part in a match-fixing scandal.
They are three points ahead of Mantova, who beat Lecce 4-0. Napoli, also on 40 points, will draw level with Juve if they beat Arezzo on Sunday.
Juventus took control of the match with early goals by Pavel Nedved and Federico Balzaretti.
Italy international Del Piero grabbed his first goal on the stroke of halftime, jinking round a defender on the edge of the area before firing in a low left-footed shot.
He scored another at the end of a solo run midway through the second half and completed his hat-trick in the 79th minute, after being put through by strike partner David Trezeguet.
Ronaldo was making his first appearance in the Milan starting line-up