The Spanish veteran and former WRC champion made the most of terrain on the 533km loop around Salta that was well-suited to his buggy, taking his second stage win of this year's race and the 27th of his career.
"The special was quite good for us, with a very fast course but a very technical sector as well," said Sainz.
"In all honesty, everything went smoothly, and from now on we'll be following this strategy: trying to win all the remaining stages until Valparaíso."
Sainz was also aided by the woes of Stephane Peterhansel - who not only suffered a puncture, but also had to slow down several times due to herds of llamas wandering onto the course.
Nasser Al-Attiyah also ran into trouble, taking a wrong turn that saw him finish second on the stage, four minutes 24 seconds behind Sainz.
Peterhansel was third quickest, but his problems meant that he only took 1:52 out of the lead of overall leader Nani Roma, who is racing "at 90 per cent" during the second week in order to preserve his lead.
Giniel Villiers consolidated his third place overall despite losing 16:25 to Sainz, as fourth-placed Orlando Terranova made a series of navigation mistakes on the seventh stage.
Nicolas Casale won the seventh stage of the quads race by 7:40 from Sebastien Husseini, with overall leader Sergio La Fuente in third place a further minute back to stay in charge of the race.
And in the trucks race, Eduard Nikolaev's trio won the seventh stage by 3:45 from the fellow Kamaz truck of Dmitry Sotnikov and his crew, though overall leader Gerard de Rooy was just 49 seconds further back to keep his stranglehold on the race.
Cars - stage seven result
1 Carlos Sainz (ESP) 4:43:28
2 Nasser Al-Attiyah (QAT) 4:48:13 +04:45
3 Stéphane Peterhansel (FRA) 4:50:54 +07:26
4 Nani Roma (ESP) 4:52:24 +08:56
5 Krzystof Holowczyc (POL) 4:54:19 +10:51
6 Federico Villagra (ARG) 4:56:22 +12:54
7 Vladimir Vasilyev (RUS) 4:59:26 +15:58
8 Giniel de Villiers (RSA) 4:59:53 +16:25
9 Orlando Terranova (ARG) 5:01:28 +18:00
10 Bernard ten Brinke (NED) 5:03:32 +20:04
1 Nani Roma 27:03:52
2 Stéphane Peterhansel + 31:31
3 Giniel de Villiers + 48:23
4 Orlando Terranova + 54:34
5 Nasser Al-Attiyah + 1:18:03
6 Carlos Sainz + 1:50:42
7 Marek Dabrowski + 2:30:47
8 Krzystof Holowczyc + 2:30:52
9 Federico Villagra + 2:52:57
10 Christian Lavieille + 3:07:06