La Rojita edged out Ukraine for top spot in Group B, while the Swiss scraped through by the skin of their teeth as runners-up in a closely-fought Group D.
Match preview
Both Spain and Ukraine may have already assured of places in the last eight before their Group B finale, but neither manager would have allowed a shred of complacency to creep in with first place and a potentially more favourable draw in the quarter-finals at stake.
Spain boss Santi Denia did not hesitate to ring the changes, though, and La Rojta went behind twice to Bogdan Viunnyk's header and Georgiy Sudakov's penalty, but they responded on both occasions through an Ivan Zhelizko own goal and a last-gasp Abel Ruiz equaliser in Tuesday's thrilling 2-2 draw.
With the two table-toppers level on points, head-to-head results and goals scored in head-to-head matches, Spain were indebted to their overall superior goal difference - +4 compared to Ukraine's +3 - as they nervously held on for first place; good thing too, as Ukraine's reward for finishing second is a taxing task against France.
Barring a failed qualification period in 2015, Spain have progressed to the semi-finals of the Under-21 Euros in each of their last five appearances in the finals - lifting the trophy aloft in 2011, 2013 and 2019 - and not since the 1990 edition have La Rojita been sent packing in the last eight.
Having now strung together a 17-game unbeaten run in all tournaments, a repeat of that scenario 33 years later seems highly unlikely on paper, as Spain seek to flaunt their attacking dominance against the side with the worst goal difference to qualify for the last eight.
France's authority in Group D was never going to be called into question, and Les Bleuets rounded off a perfect group-stage campaign with a 4-1 thrashing of Switzerland on matchday three, leaving the Rossocrociati's fate in the hands of Italy and Norway.
The Scandinavian side stunned the Azzurrini in a 1-0 success to leave all of Switzerland, Italy and Norway on three points, meaning that the tie-breakers came into effect, and the Swiss squeaked by courtesy of their superior head-to-head goals, having netted twice against both nations earlier this month.
Coming from behind to sink Norway 2-1 on the opening day would prove priceless for Patrick Rahmen's team, who will become just the third Switzerland side to strut their stuff in the Under-21 Euros quarters, and the Rossocrociati have never been knocked out at this stage before.
Indeed, Switzerland progressed to the semi-finals as hosts in 2002 before losing the 2011 final to upcoming foes Spain, and they only made their return to the big time with a group-stage exit in 2021, but a penchant for shipping goals will do them no favours on the Bucharest soil.
Rahmen's crop have already conceded eight times at the tournament so far - the most out of all 16 teams to make it to the finals - and they have failed to prevail in any of their last five meetings with Spain, most recently coming out on the wrong end of a 3-2 scoreline in a March friendly.
Spain Under-21s European Under-21 Championship form:
W
W
D
Spain Under-21s form (all competitions):
Switzerland Under-21s European Under-21 Championship form:
W
L
L
Switzerland Under-21s form (all competitions):
Team News
After making wholesale alterations for the draw with Ukraine, Spain boss Denia will revert to a more familiar setup on Saturday, and the 49-year-old is blessed with a full complement of players to select from.
Goalkeeping duo Julen Agirrezabala and Leo Roman were both granted 45 minutes of action on Tuesday, but Barcelona's Arnau Tenas will no doubt regain possession of the gloves here, while Jon Pacheco and Aitor Paredes should return to the heart of the backline.
Sergio Gomez, Abel Ruiz and Alex Baena are also set for immediate recalls, but Celta Vigo wonderkid Gabri Veiga has only been given minutes as a substitute so far and may be forced to accept another cameo appearance here.
As for Switzerland, Rahmen should also have every one of his troops available for the quarter-finals, but Dan Ndoye and Kastriot Imeri were both cautioned against France and will miss any potential semi-final if they go into the book here.
However, with the duo netting four of the Rossocrociati's five goals at the Euros so far with two apiece, their spots in the starting lineup are in no real danger, while Parma's Simon Sohm - one of two players in the squad to play their football outside of Switzerland alongside Darmstadt striker Filip Stojilkovic - could reinforce the midfield in place of Fabian Rieder.
Spain Under-21s possible starting lineup:
Tenas; V. Gomez, Paredes, Pacheco, Miranda; Baena, Blanco; Sanchez, Sancet, S. Gomez; Ruiz
Switzerland Under-21s possible starting lineup:
Saipi; Blum, Stergiou, Amenda, Omeragic; Jashari, Sohm; Males, Imeri, Ndoye; Amdouni
We say: Spain Under-21s 3-1 Switzerland Under-21s
It is not always curtains for Switzerland if they concede first, but a Spain outfit replete with attacking firepower should have no trouble exposing their opponents' defensive shortcomings.
Having also been afforded the luxury of resting their biggest names, we can only envisage La Rojita strolling into the last four with a convincing triumph.
Data Analysis
Our analysis of all available data, including recent performances and player stats, suggests the most likely outcome of this match is a Spain Under-21s win with a probability of 73.03%. A draw has a probability of 16.1% and a win for Switzerland Under-21s has a probability of 10.84%.
The most likely scoreline for a Spain Under-21s win is 2-0 with a probability of 10.94%. The next most likely scorelines for that outcome are 2-1 (9.35%) and 3-0 (9.07%). The likeliest drawn scoreline is 1-1 (7.52%), while for a Switzerland Under-21s win it is 1-2 (3.21%).