SUB Zoran Lesjak's stunning 87th-minute leveller denied Roberto Di Matteo's men a brace of Balkan victories.
Craig Beattie opened the scoring in the 12th minute of the Baggies' final tour game with a terrific right-foot finish.
But Varteks, who knocked Villa out of the UEFA Cup seven years ago, drew level seven minutes later when former Croatia international Miljenko Mumlek curled home a sublime 20-yard free-kick.
The Croatian top-flight outfit provided a sterner test than NK Nafta three days earlier but Albion deservedly regained the lead when Beattie polished off a slick breakaway move eight minutes after the break.
Albion appeared to be cruising to victory - until Lesjak spotted Scott Carson just off his line and brilliantly chipped the ball home off the underside of the bar from 25 yards.
Head coach Di Matteo rang three changes for the final game of the team's tour, with Carson and fit-again duo Gianni Zuiverloon and Beattie coming in for Dean Kiely, Abdoulaye Meite (illness) and Simon Cox (ankle).
Robert Koren also made the bench for the first time in pre-season after shrugging off tendonitis in his right knee.
The hosts, only a week away from the start of their league season and therefore much more advanced in their preparations, flew out of the blocks.
Sasa Hojski caught Jonathan Greening in possession and teed up the impressive Mumlek, who shot just wide of Carson's left-hand post from 20 yards.
Just a minute later, Carson, on his first pre-season outing, showed a strong pair of hands to push lone striker Andrej Vuk's stinging shot from the edge of the box to safety.
Albion slowly settled into the game and Zuiverloon would have been one-one-one with keeper Denis Krklec had he been able to control Marek Cech's far-post cross.
The Baggies had the ball in the net TWICE in the 12th minute, although only one of the 'goals' counted.
Beattie polished off a slick Baggies move involving Chris Brunt and Youssouf Mulumbu by volleying home at the far post, only for his effort to be ruled offside.
The Scotland international was not best pleased with the decision - but he was all smiles again within a matter of seconds.
Varteks immediately lost possession from their free-kick when Cech closed down Nikola Tkalcic, allowing Beattie to race through and smash home from 15 yards, with his effort taking the slightest deflection off the recovering Tkalcic.
The bizarre opening to this game continued in the 17th minute when Carson was penalised for collecting Zuiverloon's back-pass.
Mumlek played the indirect free-kick, positioned on the right-hand angle of Albion's six-yard box, back to Hojski whose low first-time drive was hacked off the line by Leon Barnett.
But the Balkan club were level two minutes later.
Mulumbu gave away a free-kick 20 yards out - and was subsequently booked for hacking the ball away in anger - and Mumlek gave Carson no chance with a sublime set-piece which curled just inside his left-hand post.
Albion should have been ahead again on 22 when Andrija Balajic inexplicably gifted Brunt possession 20 yards out.
The Northern Ireland international raced into the box before seeing his weak finish blocked by keeper Krklec.
It was Varteks' turn to rue a missed opportunity five minutes later when the unmarked Sandro Bloudek shot wastefully over from Vuk's centre.
Back came Albion and Dino Skvorc needed a moment to clear his head after feeling the full force of Brunt's 30-yard free-kick.
The temperature in Varazdin was much cooler than at Wednesday's game in Lendava, Slovenia, and the Baggies even had the luxury of a refreshing rain shower.
Di Matteo's side created another golden opportunity just before half-time when Mulumbu sliced open the Varteks defence with a sublime throughball.
Moore raced clear and was only denied a second goal in as many games by Krklec's outstretched boot.
Di Matteo rang three changes at the break, with Barnett, Dwayne Samuels and Moore making way for Shelton Martis, Borja Valero and Filipe Teixeira.
Albion dominated possession at the start of the second half and deservedly snatched a 53rd-minute lead.
Greening beat the offside trap to race onto Zuiverloon's defence-splitting pass and drew sub keeper Sasa Dreven before unselfishly squaring to Beattie, who slid the ball into the empty net.
That proved the former Celtic striker's final contribution and he was afforded a warm reception by the home fans when he made way for Chris Wood on 61.
Albion were now in total control and Teixeira was only a whisker away from giving the tourists a two-goal cushion when he raced on Brunt's diagonal ball and fizzed an acute 15-yard drive past the far post.
With Albion happy to play long spells of keep ball, chances became few and far between, although the Baggies always looked dangerous on the break.
Koren was given his first taste of pre-season action when he replaced Greening six minutes from time.
But Albion were denied a second successive victory when Lesjak levelled on 87.
NK VARTEKS (4-2-3-1): Krklec (Dreven HT); Tkalcic, D Skvorc, Prahic (Susac 58), Balajic; Radicek (Lesjak 58), Jagacic (Simek 73); Hojski (Conjar 73), Mumlek (C) (F Skvorc 81), Bloudek (Hasija 67); Vuk (Frljuzec 61).
ALBION (4-4-2): Carson; Zuiverloon (Worrall 67), Barnett (Martis HT), Olsson, Samuels (Valero HT); Brunt (Kim 73), Greening (C) (Koren 84), Mulumbu (Labadie 76), Cech; Moore (Teixeira HT), Beattie (Wood 61). Sub not used: Daniels (GK).
GOALS: NK VARTEKS - Mumlek (19), Lesjak (87). ALBION - Beattie (12, 53).
BOOKINGS: ALBION - Mulumbu (kicking ball away 18), Cech (unsporting behaviour 89).
REFEREE: M Zebec (Lovrecan, Croatia)
ALBION STARMAN: Craig Beattie.
