Scorers: Luzern - Schneuwly (68); St Johnstone - MacLean (48)
The Scottish Cup winners found themselves under the cosh in the first half in Switzerland but stunned the hosts two minutes after the break when MacLean prodded home from eight yards.
Marco Schneuwly drew the Swiss Super League outfit level with 21 minutes remaining but it was another impressive performance by the McDiarmid Park men on the continent.
Saints had to rely on the same squad that won their first major trophy with that historic 2-0 win over Dundee United at Celtic Park just two months ago.
Injuries meant defender Steven Anderson and midfielder Gary McDonald did not even board the plane to Switzerland, and to further tie the manager’s hands together, last season’s 27-goal top scorer Stevie May was limited to a place on the substitutes’ bench after failing to shake off a thigh strain.
That meant Tommy Wright had to go with MacLean as his loan striker, but Saints were comfortable in the opening stages.
Saints were having to work hard amid temperatures of 32 degrees Celsius but survived with their clean sheet intact until the break.
Luzern would have been confident of eventually breaking down their opponents but within two minutes of the restart they were behind. They failed to clear a Saints corner and left MacLean unchecked as he got on the end of David Wotherspoon’s assist to prod home.
Saints’ luck did not last though and Schneuwly did find the net for Luzern as he was allowed to turn in the box and fire inside Alan Mannus’s right-hand post.
Luzern: Zibung, Rogulj, Lustenberger, Thiesson, Affolter, Wiss (Lezcano 60), Doubai (Bento 60), Hyka (Bozanic 75), Winter Freuler, Schneuwly. Subs not used: Bucchi, Holenstein, Hochstrasser, Sarr.
St Johnstone: Mannus, Mackay, Wright, Caddis (O’Halloran 75), Miller, Brian Easton, Millar, Wotherspoon, Brown, Croft (Scobbie 89), MacLean. Subs not used: Banks, May, Rodger, Kane, Dylan Easton.