Juve missed the chance to go nine points clear at the summit as Franco Brienza's second-half equaliser rescued a 2-2 draw for Cesena.
The reigning champions looked set to take all three points when Arturo Vidal stepped up to take an 82nd-minute penalty, but the Chile star missed the target, leaving Juve to rue not capitalising on Roma's 0-0 draw with Parma earlier in the day.
Cesena's battling display gave little indication of their precarious position in the relegation zone, with Milan Djuric giving the hosts a deserved lead 17 minutes in, before Alvaro Morata levelled soon after.
The Colombian was straight in the action as he was fouled for Xherdan Shaqiri's second-minute penalty, before Maximiliano Moralez restored parity with just under half an hour played.
But Guarin then intervened with his first goal before the break, curling superbly into the bottom corner.
Yohan Benalouane’s red card just after half-time did not help Atalanta's chances and Guarin then hit home an even better strike shortly after, with Rodrigo Palacio rounding off the win 18 minutes from time.
Empoli came from behind to claim a deserved 1-1 draw at 10-man Milan after Mattia Destro had given the hosts the lead with his first goal for the club.
