With less than three minutes on the clock during their opening continental battle of the season, Sparta Prague silenced a near 20,000-strong Allianz Stadion home crowd as Krejci II headed home, but the 36-time Czech champions failed to shut up shop and paid the price for it.
Former Bayern Munich and Inter Milan youth product Knasmullner took centre stage with two quickfire goals in the 63rd and 70th minutes of the encounter in Vienna as the Austrian side claimed a priceless first-leg advantage, and Krejci II's away goal does not hold the same significance that it would have done 12 months ago.
Nevertheless, Pavel Vrba's side dusted themselves down to kick off their Czech First League campaign with a 3-2 success over Sigma Olomouc on Saturday, with the capital side seeking their first top-flight title since 2014 following seven years of Slavia Prague and Viktoria Plzen dominance.
Not since the 2005-06 campaign have Sparta Prague dined at Europe's top table in the group stage, as the third-round curse befell them three years in a row between 2014 and 2016, and Vrba's men will need to bring their stellar domestic home form to the continental stage if they are to turn the tie around this week.
Including friendlies, Sparta Prague have won 15 of their last 17 encounters in the Czech capital - with the only loss in that sequence coming against neighbours Slavia in the cup - but Rapid Vienna are the ones holding all the cards.
Sparta's upcoming opponents Rapid Vienna suffered contrasting fortunes continentally and domestically, as unlike the Czech side, they kicked off their top-flight campaign with a 2-0 defeat to TSV Hartberg at the weekend.
Two strikes either side of the half-time whistle from Dario Tadic condemned Dietmar Kuhbauer to the worst possible start to their 2021-22 Bundesliga campaign, and fans were disappointed not to see their team turn a corner after the summer break, with Rapid Vienna losing three of their last four league games last term.
However, the 32-time Austrian champions - who have not tasted national glory since 2008 - are in the driving seat when it comes to their Champions League endeavours, and as was the case with Sparta, Rapid last reached the group stage in the 2005-06 campaign, where Bayern Munich and Juventus quickly sent them packing.
Whichever side ultimately produces the goods on Wednesday may see their Champions League dreams come to a bitter end, however, as Ligue 1 powerhouses Monaco lie in wait for the victors during August's third round.
Sparta reported no fresh injury concerns from their recent domestic and continental showdowns, but some alterations may be afoot for their third encounter in the space of a week.
Teenage sensation Adam Hlozek failed to fire on the opening weekend, but Krejci II has found a goalscoring spark of his own after netting his side's second of the afternoon against Olomouc at the weekend.
David Moberg-Karlsson was on target in league action and could force his way into the first XI over the more defensively-minded Tomas Wiesner, with Sparta needing to adopt a gung-ho approach to have any chance of advancing.
Meanwhile, Rapid Vienna lost midfielder Srdjan Grahovac to injury after just 22 minutes at the weekend, and the 28-year-old is now confirmed to be missing several weeks with facial fractures.
Grahovac is joined in the infirmary by fellow absentees Philipp Schobesberger and Dalibor Velimirovic, but Robert Ljubicic - who is serving a domestic ban - can return for European competition and fill the void in the engine room.
Kelvin Arase replacing Thorsten Schick out wide may be the only other change that the visitors make from the weekend, although Ercan Kara's place up top could soon come under threat from Taxiarchis Fountas.
Sparta Prague possible starting lineup:
Nita; Vindheim, Stetina, Hancko, Holer; Moberg-Karlsson, Krejci II, Pavelka, Krecji; Dockal; Hlozek
Rapid Vienna possible starting lineup:
Strebinger; Stojkovic, Wimmer, Hofmann, Ullmann; Ljubicic, Petrovic; Arase, Knasmullner, Grull; Kara
We say: Sparta Prague 1-1 Rapid Vienna
Sparta's enthralling league victory was the perfect tonic after their first-leg defeat, whereas Rapid Vienna's confidence has been rocked a tad after their domestic season kicked off in poor fashion.
However, the Austrian side should still dig deep enough to claim a draw and book their spot in the next round, but Monaco will certainly provide a step up in class.
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