Pastore netted in the 18th minute and fellow Argentine Angel Di Maria doubled the tally in the 77th before Ibrahimovic wrapped up the victory six minutes from time to put PSG on 17 points from seven games after two consecutive draws.
They lead Stade Rennes and St Etienne who have 13 points and play on Wednesday at Ajaccio and Troyes respectively.
Ibrahimovic, whose start to the campaign has been hampered by injuries, missed from the spot in the 87th minute.
Pastore opened the scoring with a low shot from just inside the box, after being set up by Ibrahimovic, as PSG were rewarded for their early domination.
Unbeaten in Ligue 1 since March 15, the side from the capital were barely threatened by Guingamp, who had their best chance just before the interval when Yannis Salibur's fierce strike was parried away by Kevin Trapp.
Di Maria, who had been quiet for most of the game popped up to score his first league goal of the season after Guingamp keeper Jonas Lossl dropped the ball having blocked Ibrahimovic's shot leaving the Argentine to poke home for 2-0.
Ibrahimovic then collected Di Maria's cross on the left side of the area and beat Lossl to put the result beyond doubt.
The Sweden striker, however, saw his weak penalty tipped away by Lossl after Guingamp had been punished following Younousse Sankhare's foul on Edinson Cavani.
Stade de Reims and Angers are fourth and fifth respectively on 12 points after a 0-0 draw earlier on Tuesday.
(Reporting by Julien Pretot; Editing by XXXX)
