It started well for Sweden, who took the first set 21-18. It was also Slovenia's first set loss in the European League this season.
But then things started to get worse and worse for the Swedish side. Slovenia levelled after 25-21 in the second set and also took the lead when they won the third set 25-17.
Star Isabelle Haak played brilliantly, and after a dramatic finish, Sweden levelled the match at 2-2.
The match was close, but Sweden, led by Haak, pulled ahead, winning the fifth set 15-13 and the match 3-2.
The return leg will be played away on Saturday. Slovenia must win it to take the European League final to a Golden Set (to 15 points) to determine this year's champion nation.
