Inter Milan saw its seven-match winning streak 0 win.
The goal arrived from a Massimo Oddo ball into the penalty area that Giacomazzi brought down and fired past goalkeeper Julio Cesar on the turn.
Inter cranked up the pressure in the second half and had two goals called back for offsides before a string of saves from Lecce goalkeeper Massimiliano Benassi preserved the win.
The first stop denied Ricardo Alvarez before he made another save on Maicon. But the best effort of the day came in the game's final minute as Benassi reacted well to keep out a close-range header from Giampaolo Pazzini following an Alvarez free kick.
Lecce remains in the bottom three but moves to within three points of safety having collected seven points from its last three matches.
Inter drops back to fifth place and nine points off the pace of leaders Juventus.
Milan, Italy - Zlatan Ibrahimovic scored his Serie A-high 15th goal and added an assist, as AC Milan rolled to a 3-0 win over Cagliari on Sunday at the San Siro to move back within one point of Serie A leader Juventus.
Ibrahimovic scored off a free kick after 32 minutes, then chested down a pass for Antonio Nocerino to hammer home for his seventh goal in the 39th.
Massimo Ambrosini added an insurance goal in the 75th, as Milan clinched its fifth win in its last six. The defending Serie A champions are second on 43 points behind unbeaten leader Juve.
Cagliari lost for the third time in its last six as it slipped to 13th with just 23 points from 20 matches.
Fiorentina 2, Siena 1
Florence, Italy - Fiorentina claimed its second win in seven matches on Sunday with a 2-1 home triumph over Siena.
Stevan Jovetic notched the opening goal after four minutes and Cesare Natali doubled the lead shortly after the hour mark for the Viola.
Emanuele Calaio handed Siena a chance to get back into the game with a penalty kick in the 89th minute following a handball from Matija Nastasic, but the hosts held out for all three points and move nine points clear of the drop zone, with Siena sitting only three points above the bottom three.
Atalanta 1, Cesena 0
Cesena, Italy - Atalanta ended a three-match losing streak on Sunday as Marco Rossi's own goal gave the visitors a 1-0 win at Cesena.
A cross from Ezequiel Schelotto in the 76th minute was deflected by Rossi into his own net, but Cesena was given a chance three minutes later when Atalanta's German Denis received a second yellow card.
Substitute Jorge Martinez had the best chance over the final 10 minutes when his shot from eight yards in the dying moments was kept out by goalkeeper Andrea Consigli, dealing Cesena its fifth loss in six matches.
Lazio 3, Chievo 0
Verona, Italy - Lazio climbed into the top four on Sunday after notching a 3-0 win at Chievo that moves the club to within two points of third-place Udinese.
Edy Reja's side had lost two of its last three games but started well with Hernanes putting the visitors ahead after 21 minutes.
The teams remained separated by just one goal until the final minutes, when Lazio's Miroslav Klose tallied two late goals to seal the win and move his team past Inter Milan.
Chievo is 12th following the loss, which is the club's second in four games.
Genoa, Italy - Two goals from Rodrigo Palacio helped Genoa to a 3-2 win over Napoli on Sunday at the Luigi Ferraris Stadium as the hosts survived a late scare to remain in the top half of the league.
Genoa entered the contest having lost three of its last four games, but got off to a fantastic start as first-half strikes from Palacio and Alberto Gilardino put the hosts up two goals at the break.
Palacio appeared to wrap up the points with his second goal of the match 20 minutes from time, but Napoli rallied to pull to within a goal in the final 10 minutes as Edinson Cavani and Ezequiel Lavezzi scored three minutes apart.
The rally fell short, however, and Napoli saw its four-game unbeaten streak come to an end.
Palermo 2, Novara 0
Palermo, Italy - Palermo dealt last-place Novara its fourth successive defeat on Sunday as two goals from Igor Budan gave the hosts a 2-0 win at the Renzo Barbera.
Fabrizio Miccoli played provider on both of Budan's goals, with the first coming four minutes before halftime on a header.
Palermo had lost two of its previous three contests, but another header from Budan in the 72nd minute after Miccoli's cross secured the win and keeps the club in the top eight.
Novara is seven points from safety and looks to be facing a real battle to stay in the top flight.
Roma 1, Bologna 1
Rome, Italy - Roma saw its run of four straight wins in Serie A come to a halt at the Stadio Olimpico on Sunday as bottom-half side Bologna claimed a 1-1 draw.
Marco Di Vaio gave the visitors the lead in the 56th minute, with Roma answering through Miralem Pjanic six minutes later to salvage a point.
Both sides had chances to snatch the win, but both had to settle for a point, which gives Bologna three successive draws and moves the club five points clear of the bottom three.