Marco Silva's men had been looking to kick-start their campaign after drawing their league opener at Academica a week earlier and the morale-boosting triumph they craved arrived in second-half stoppage time.
Nani, who was greeted with a rapturous welcome, made his second debut for his boyhood club after he returned on loan from Manchester United as part of Marcos Rojo's move to Old Trafford.
However, his day did not completely go to plan.
The Portugal international impressed in flashes on the flank but he saw his 63rd-minute spot-kick saved by goalkeeper Mauro Goicoechea, much to the displeasure of usual penalty-taker Adrien Silva.
Nani was eventually replaced by Junya Tanaka and the Japanese attacker played a crucial role in the winning goal as he shot against the post in the 93rd minute and Carlos Mane, another substitute, tapped in the rebound.
There was no such late panic for Porto, though, as a 1-0 victory at Pacos Ferreira continued Julen Lopetegui's winning start in charge.
Porto received an early blow as Cristian Tello was forced off with a thigh injury after just 20 minutes.
The change did not prove to be particularly detrimental, however, as Tello's replacement Juan Quintero set up Jackson Martinez for the only goal of the game in the 40th minute.
The young midfielder lofted a deep cross in from the left and Martinez coolly struck a first-time effort across goal and into the bottom-right corner.
The only other match on Saturday saw Maritimo pick up their first victory of the campaign, as they defeated visitors Academica 2-1.
Rui Pedro's 83rd-minute goal gave the hosts something to worry about late on but in the end they had already done enough.
A quick-fire double at the beginning of the second half from Fransergio and Moussa Maazou initially opened up a two-goal advantage and they held on for a narrow victory, a first for new coach Leonel Pontes.
