Having already caused a stir around Europe by knocking out Norwegian heavyweights Rosenborg, the Perth outfit followed that feat up with an impressive success in Belarus.
MacLean bagged the winner with 22 minutes left in Grodno - 140 miles west of the former Soviet state's capital, where Minsk's stadium is being redeveloped - to put Saints on course for the play-off round.
Netting the goal that booked Saints' place in the third qualifying round was not enough to keep Stevie May in the starting line-up as boss Tommy Wright opted to pack his midfield instead.
The 20-year-old striker - who struck the second-leg equaliser against Rosenborg - was replaced by Liam Caddis, while Murray Davidson took a place on the bench after re-signing with the club last week.
Visa delays and sky-high air fares meant the Scots travelled behind the former Iron Curtain with just one solitary supporter for backing.
But despite having to go it almost alone, the McDiarmid men coped well during a relatively trouble-free first 45 minutes.
Minsk midfielder Sergei Kozeka saw a decent opportunity blocked by Steven Anderson just seconds into the second half as the centre-half bravely stood his ground.
Davidson's return to the Saints side came just four minutes after the restart and the Scotland cap made an immediate impression, coming close with a pair of headed opportunities.
The hour mark brought about another decent opening for Saints as David Wotherspoon drove in from the left-hand side but Nigel Hasselbaink failed to read his low cut-back as the forward dashed into the Minsk box.
But within eight minutes St Johnstone had edged themselves in front as MacLean, collecting Liam Caddis' pass, took advantage of space in the box to shoot early on the right-hand side of the box, burying the ball under Vladimir Bukatkin.