A hat-trick from Ronaldinho guided AC Milan to a 4-0 home win over 10-man Siena on Sunday, moving Leonardo's side to within six points of Serie A league leader Inter Milan.
Ronaldinho converted a 12th minute penalty following a red card for Siena goalkeeper Gianluca Curci and Marco Borriello hit his seventh goal of the season before the Brazilian struck two more goals after the break to seal Milan's win.
"Ronaldinho scored a great goal, one of rare beauty," Leonardo said, referring to his fellow Brazilian's curling shot past Siena's substitute keeper Gianluca Pegolo from the edge of the area.
"But that's what he's like, a player who does fantastic things. It all comes down to him. If he is in the mood and determined, then he does things no one else in the world can."
Inter is top with 46 points following its 2-2 draw with Bari on Saturday. Milan is second on 40, but has a game in hand and meets Inter in the Milan derby next week.
"Now for the derby," Leonardo said. "It is an important game, but not decisive. Of course, the fact that the two teams are six points apart in the league gives it an extra edge."
AS Roma is third with 35 points after a 3-0 win at home to Genoa, Napoli moved up to fourth on 34 after 0-0 draw with Palermo, while Juventus lost 1-0 at mid-table Chievo Verona and slipped to fifth, one point further back.
Italy striker Luca Toni scored his first goals since joining Roma on loan from Bayern Munich after Simone Perrotta had opened the scoring in the 17th minute.
In the late match, Napoli missed the chance to move into third with its draw at home to Palermo. Napoli needed goalkeeper Morgan De Sanctis to save a first half penalty from Fabio Miccoli to help secure the point.
At San Siro, Milan started brightly and came close to scoring in the third minute when Alessandro Nesta crossed from the right and Ronaldinho volleyed the ball narrowly over.
However, the Brazilian made no mistake from the penalty spot just nine minutes later.
Siena defender Brandao dithered with the ball in the area, Borriello stole it and rounded Curci who brought him down. After the referee sent off Curci, Ronaldinho beat substitute Pegolo from the spot.
Siena striker Massimo Maccarone missed a great chance to level in the 26th when he forced his way through the Milan defense, but fired over with only goalkeeper Dida to beat.
Borriello made Siena pay for the miss when he volleyed in Andrea Pirlo's cross two minutes later.
Milan continued to dominate after halftime, with Ronaldinho heading home a corner taken by David Beckham in the 72nd minute and then scoring his third a minute from time.
"Today we won and we had a great game because we prepared for every eventuality," Leonardo said. "We were conscious that Siena could cause us problems and we prepared every detail for this match."
Roma took the lead in its game when Genoa's defense was unable to clear David Pizarro's cross. Juan headed back across goal and Perrotta ran in to fire home.
Toni grabbed his first goal when Mirko Vucinic cut in from the right, slipped the ball into his path and the Italy striker slid the ball under Genoa goalkeeper Marco Amelia just before halftime.
Toni added his second on the hour mark, heading home a freekick taken by Vucinic.
"The important thing is to qualify for the Champions League," Roma coach Claudio Ranieri said. "But there is still a long way to go in the championship and a lot will happen."
Paying tribute to Toni's performance, Ranieri said: "We needed a player like him, strong in the air and with presence in the penalty area. He had a great game today."
Juventus slumped to its fourth loss in five games after Gennaro Sardo scored for Chievo in the 33rd minute. Juventus' midfield gave the ball away and Sardo was quickest to react as he hit a long range shot past Gianluigi Buffon.
After the break, Juventus struggled to find any rhythm and the closest it came was a weak freekick from Alessandro Del Piero.
"It is a bad period and I don't want to make excuses," Juventus coach Ciro Ferrara said. "We conceded the goal, but didn't react in the right way. We have players who aren't in good shape and we are losing morale by not getting results," he said.
Also Sunday, it was; Atalanta 3, Lazio 0; Fiorentina 1, Bologna 2; Parma 0, Udinese 0; Sampdoria 1, Catania 1.
