The Dane took victory ahead of Nigel Melker (Tech 1 Racing) and his compatriot Kevin Magnussen (DAMS).
"It felt like a pretty long race," Sorensen said. "We weren't sure how to make our stop at the right time without taking too many risks. It seems we made the right decision.
"I'd like to thank my team for supporting me when things haven't been so good. I now can't wait to go to Budepest and see if we can continue this run."
Melker was the fastest man in qualifying, but the Dutchman had his best lap deleted for blocking Magnussen. Sorensen was duly promoted to pole, with Melker alongside him on the front row.
Championship leader Magnussen qualified in third, with his closest rival, Stoffel Vandoorne, joining him on the second row.
As the lights went out, Antonio Félix da Costa (Arden Caterham) remained glued to the grid. Sorensen held his lead from the start, with Magnussen passing Melker after Vandoorne had spun at turn one.
When the pit window opened, the majority of the drivers used the opportunity to make their stops. Melker pitted on lap seven, with Sorensen and Magnussen following two laps later. The race order remained unchanged, and Sorensen soon stretched his lead.
The Lotus driver, however, had his advantage wiped out on lap 22, after the safety car was introduced to remove Carlos Huertas' car from the track. The Carlin man's single-seater had stopped on the track following a spin.
Magnussen pushed hard after the restart, but Sorensen held on to win the race. Melker finally recorded another second place after Magnusen was penalised after his first-lap off-track overtaking.
Fourth, Sergey Sirotkin was the best-placed rookie and gained six places thanks to a late pitstop. William Buller (Zeta Corse) came fifth, followed by Marlon Stockinger (Lotus), Nico Müller (International Draco Racing), Pietro Fantin (Arden Caterham) and Norman Nato (DAMS).
RED BULL RING - RACE TWO
1-SORENSEN (DEN) – Lotus 45:42.658
2-MELKER (NED) - Tech 1 Racing - +5.422
3-MAGNUSSEN (DEN) – DAMS - +6.517
4 SIROTKIN (RUS) – ISR - +7.117
5 BULLER (GBR) - Zeta Corse - +11.004
6 STEVENS (GBR) - P1 by Strakka Racing - +12.937
7 STOCKINGER (PHI) – Lotus - +14.054
8 MULLER (SUI) - International Draco Racing - +14.416
9 FANTIN (BRA) - Arden Caterham - +16.899
10 NATO (FRA) DAMS - +18.254