Lacklustre St Johnstone wilted in Yerevan as Mihran Manasyan’s second-half strike gave Alashkert a deserved victory on their European debut.
Visiting goalkeeper Alan Mannus had already denied the Armenian side with a couple of fine saves before the striker gave them a 60th-minute lead.
The Perth side had been rarely seen as an attacking force before he thrashed the ball high into the roof of the net.
Tommy Wright’s side were stung into action but failed to threaten.
And the side who finished fourth in the Scottish Premiership will have to improve in the second leg at McDiarmid Park if they are to progress to the second qualifying round of the Europa League against either Red Star Belgrade of Serbia or Kairat Almaty of Kazakhstan.
Abraham Khashmanyan’s team started brightly and, after they forced a corner in the opening minute, Saints’ Murray Davidson received a nasty head wound as he helped clear the visiting lines.
With the midfielder off the field receiving treatment for six minutes, the Perth side were on the back foot and Mannus was called into early action to save shots from Gevorg Karapetyan and Siarhei Usenia as the home side dominated possession.
Saints eventually get their first shot on goal after half an hour against the team that finished fourth in the Armenian top flight.
Good link-up play on the edge of the box between new signing John Sutton and David Wotherspoon led to the latter’s shot being pushed around the post by Gevorg Kasparov in the home goal.
After water breaks in the searing heat, Mannus dived low to his left to tip away a shot from Narek Gyozalyan from 25 yards.
Davidson, still suffering from the earlier head knock, was replaced with Scott Brown just before half time and Saints suffered a further blow when Alashkert made their dominance tell with what was to prove the winning goal.
Winger Karen Muradyan cut the ball back from the by-line and Manasyan hammered the ball high into the roof of the net past a despairing Mannus.
Saints tried to respond and Sutton headed over from eight yards under pressure, but Wright’s side rarely threatened the home goal.
A cooling breeze began to blow through the stadium as dusk fell, but this was little help to Saints as they struggled to cope with the intense heat.
With only two minutes left, Chris Kane, who had replaced Sutton, found space on the edge of the six yard box, but the substitute striker’s effort was weak and Saints will now have to rely on winning next week’s second leg in Perth.
By Brian McLauchlin BBC Scotland in Yerevan