- Shakhtar Donetsk 1-0 Partizan Belgrade: As it happened
The Croatia captain curled home a fine free-kick 20 minutes from time to give the hosts the points from a closely-fought encounter at the Donbass Arena.
The result put Shakhtar joint top of the pool, behind Arsenal - 6-0 winners over Braga - on goal difference.
The Ukrainian champions started on the front foot but had few clear-cut chances to show for their toils.
Razvan Rat blasted a left-footed attempt wide from just outside the area in the fifth minute and Brazilian forward Willian drilled in an effort from similar distance 16 minutes later only for Vladimir Stojkovic to make the save.
Serbia goalkeeper Stojkovic again had to be alert to parry a decent shot from Luiz Adriano in the 27th minute after the Brazilian striker connected with Srna's cross.
Douglas had a free-kick just before the half-hour punched away by Stojkovic and another curling attempt parried to safety as 2009 UEFA Cup winners Shakhtar continued their fruitless pursuit of a first-half opener.
Partizan offered little going forward, Mohamed Medo's long-range effort never threatening Andrei Pyatov's goal on its way over the bar.
The match continued in much the same vein after the interval, with both teams struggling to make a difference in the final third.
Olexander Kucher lashed over the bar from 30 yards for Shakhtar and Cleo headed wide for the Serbian champions just after the hour mark.
Stojkovic remained the busier of the two goalkeepers, tipping a Luiz Adriano header over the bar from Srna's cross.
But the home fans did not have to wait too much longer to celebrate the opening goal.
Shakhtar were awarded a free-kick 25 yards out when Milan Smiljanic fouled Alex Teixeira, and Srna stepped up to curl past a helpless Stojkovic and into the bottom-left corner.
That sparked Partizan into action, with Pyatov twice in the space of a minute forced to pull off fine saves to preserve his side's lead.
He first tipped a Sasa Ilic blast around the post and then did likewise with Nemanja Tomic's effort, but the equaliser was not forthcoming.