Domínguez began the day 39.4sec clear of the Briton and maintained his advantage through a tricky morning in which changing grip, loose rocks and the lingering threat of rain kept crews guessing.
His day was made slightly more complicated by an unusual problem when he accidentally left his glasses on the roof of his Toyota GR Yaris Rally2 after SS10.
Domínguez completed the following stages without them before his mother and wife sourced a replacement pair from a local optician during midday service.
“I’d rather drive with my glasses on!” he admitted after Trinidad. “For sure I am losing confidence without my glasses.”
Greensmith had his own difficulties, spending much of the morning battling a worsening brake problem which left the pedal dropping towards the floor.
Despite that, he remained within striking distance and began eating into Domínguez’s advantage as Saturday progressed.
The gap was reduced to 20.4sec after the afternoon pass of Trinidad, where Greensmith took 6.8sec out of the leader despite brushing a tree stump.
A trip off the road on the day-ending Encarnación Costanera super special cost Greensmith several seconds, allowing Domínguez to restore his cushion slightly to 24.3sec overnight.
Domínguez, meanwhile, was greeted by another enormous home crowd as he completed the mixed-surface test.
“Just unbelievable, the amount of fans and the passion they have,” he said. “Incredible, really. No words.”
Behind the leading pair, Fau Zaldivar produced an impressive recovery to climb into third place.
The Paraguayan had seen his hopes of fighting at the front damaged by a puncture on Friday, but reset on Saturday and rediscovered his pace, including a strong run through the second pass of Trinidad.
“After yesterday we needed to clear our heads,” he explained. “Today was about restarting and showing some good pace.”
Zaldivar ends the day 1min 13.2sec behind Domínguez, giving the home support two Paraguayan crews inside the WRC2 top three.
Alejandro Galanti makes it three in the top four at 2min 59.3sec, although he has Taylor Gill just 1.9sec behind him heading into Sunday.
Yohan Rossel is sixth, 4min 39.4sec from the lead after a difficult rally so far.
Saturday also removed two potential challengers from the sharp end. Romet Jürgenson crashed on the first pass of Hohenau while running strongly inside the WRC2 top five, while Marco Bulacia stopped on the following Trinidad stage.