Wouter Vrancken conceded that Hearts' inability to defend set-pieces against Sturm Graz has given his team a mountain to climb to keep their Champions League hopes alive. 

Hearts were thumped 4-0 at Stadion Graz-Liebenau on Tuesday in the first leg of their second qualifying round tie for the Champions League. 

Jon Gorenc Stankovic headed Sturm Graz into a fourth-minute lead from Jeyland Mitchell's long throw before the full-back got himself on the scoresheet in the 50th minute. 

Mitchell's goal came from another set-piece, this time from Otar Kiteishvili's corner, with Luca Weinhandl pulling Sturm Graz further ahead three minutes later.

The rout was concluded by Jurgen Heil just before the hour, though Hearts had their chances to reduce the deficit ahead of next week's second leg at Tynecastle.

Hearts finished with an expected goals (xG) total of 1.68 from their 19 shots to Sturm Graz's 2.28 from one more attempt, though Vrancken was left to bemoan two lapses in concentration that cost his side. 

"We didn't start too badly but then lost the [goal from the] set piece. Our game got killed by two set-pieces first half and second half," Vrancken said. 

"After the first goal, we needed some minutes to come back into it and find our confidence again.

"But then we did well and created a lot of chances. We have to do a lot better with these chances. At this level you have to score goals there.

"I was confident at half-time that we could still turn it around, that we could use the space better and show more conviction.

"Then the second half starts. We get the first good opportunity, but we miss it. Then we concede from a set-piece and mentally it's difficult for the players.

"Then the players want to force it and lose the overview and make it more difficult."

Landry Kabore and Alexandros Kyziridis squandered excellent first-half opportunities for Hearts, who endured a difficult first competitive outing under Vrancken. 

It's been a summer of change for Hearts, who, after losing out on their first Scottish Premiership title since 1960 on the final day of last season, have seen former boss Derek McInnes, striker Lawrence Shankland and Cammy Devlin all depart for Rangers. 

Hearts now look highly likely to drop into the Europa League, where they would face Marco Silva's Benfica or St. Gallen.

Defeat in that encounter would leave them needing to win a Conference League play-off to achieve league phase football.