Neuville entered the pair of mile-long stages seven seconds clear of Elfyn Evans' Ford, but more than doubled that advantage over two runs with the fastest time on both occasions.
Evans completed two conservative runs on the hard tyres he had selected earlier in the day, while Neuville efforts were completed on softs - allowing the Belgian to extend his lead to 17.7s.
Kris Meeke did his street stage runs on three tyres, with his left-rear wheel down to the rim after a tyre had delaminated on the final stage of the afternoon loop, leaving him without another undamaged tyre.
Portugal Rally
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20/05/2018 AT 18:05
Having started the stages a provisional third, Meeke lost more than half a minute to Neuville on each run and is now eighth overall, 1m18.7s off the lead.
That allowed Neuville's Hyundai team-mate Dani Sordo back into the overall podium places.
The Spaniard took two stage runner-up spots - ending up 0.4s and 0.1s respectively away from Neuville - and is now 24.3s shy of the lead.
Teemu Suninen and Mads Ostberg both contested the Porto stages after they were held up on SS7 behind the Hyundai of Hayden Paddon - who was airlifted to hospital - before the stage was stopped.
Suninen and Ostberg now occupy fifth and seventh respectively in the order, after they were both given notional SS7 times following its stoppage.
The sole remaining Toyota of Esapekka Lappi struggled as a result of rear damper damage, which caused his car to bump up and down aggressively on the stage.
Lappi also had a spin, losing 12.8s to Neuville over his two runs, and is sixth overall - 45.8s off the lead.
Portugal Rally
Neuville on brink of Portugal victory
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Portugal Rally
Neuville continues to build Rally Portugal lead
19/05/2018 AT 18:03