The playmaker was in inspired form as goals from Edinson Cavani, Marco Veratti and Gregory van der Wiel gave the home side the win
The Parisiens - aiming for their third successive league title - started the day goal difference behind Lyon, but took advantage of their game in hand against a Metz side who now appear doomed in their fight for top-flight survival.
Goals from Marco Verratti and Edinson Cavani before the break put Laurent Blanc's side in control, but Modibo Maiga's 53rd-minute header gave Metz a lifeline.
However, the hosts extinguished any chance of a comeback from the visitors through Gregory van der Wiel's second half strike to put the pressure back on Lyon.
Metz - unbeaten in four matches but still eight points adrift of safety - made a good fist of the first 15 minutes, only for Ezequiel Lavezzi's darting run to provide the flicker of encouragement the hosts needed.
Lavezzi, who ran at the Metz defence and beat multiple players, saw his pass turned over by Blaise Matuidi, but the move lifted PSG - missing injured pair Salvatore Sirigu and Serge Aurier - who took the lead seven minutes later through Verratti.
Pastore, who starred and contributed all three assists, was given too much time on the ball and played Verratti in with a simple pass which allowed the Italy international to take a touch before slotting into the bottom-left corner from just inside the penalty area.
Cavani could have doubled their lead 10 minutes before the break, but could not get the ball out from under his feet, although the disappointment did not last long.
The Uruguay star brought the Parc des Princes crowd to their feet in the 42nd minute after winning the ball in midfield, finding Pastore and continuing his run forward.
Pastore returned the pass and Cavani did not have to break stride, bursting through Metz's defence with pace and power before dinking over goalkeeper Anthony Mfa Mezui.
Bouna Sarr thrashed over for the visitors after the restart and Albert Cartier's men then silenced the home crowd when Maiga netted to give the strugglers a glimmer of hope.
Sarr did most of the work, storming down the right after beating David Luiz and producing a pin-point cross that Maiga, free of Thiago Silva, simply nodded in off the left-hand post.
Cavani could have restored the two-goal advantage but fired straight at Mfa Mezui from an angle, while at the other end, Florent Malouda should have done better on a counter-attack, with his tame effort easily saved by back-up PSG goalkeeper Nicolas Douchez.
Van der Wiel then made sure of the three points with 13 minutes left as PSG moved two points clear at the top of Ligue 1.