Real Madrid scrape past third-tier Talavera in Spanish Cup
Talavera may be only 100km from the Spanish capital but their modest 6,000-capacity Estadio El Prado is a world away from Real's Santiago Bernabeu fortress.
Yet Alonso's 20-time Cup winners only narrowly avoided a potential banana skin.
Mbappe opened the scoring from the spot and Manu Farrando's own goal in first-half injury time put the regal visitors in control at the break.
But Nahuel Arroyo's 80th-minute goal for the modest hosts set up a nerve-tingling ending.
Mbappe fired in from outside the box with two minutes left on the clock only for Gonzalo Di Renzo to score in the first minute of injury time as Talavero went down fighting.
Elsewhere, high-flying La Liga outfit Villarreal came unstuck 2-1 at second-tier Racing Santander.
Aanother second-division club Albacete celebrated knocking out La Liga's Celta Vigo 3-0 on penalties after the two sides were locked together 2-2 after extra time.
Fourth-tier outfit Baleares fell to a valiant 3-2 defeat against 10-time Cup winners Atletico Madrid in the Mallorcan capital of Palma.
Another Liga side Osasuna needed extra time to see off second-tier Huesca 4-2.
On Tuesday, Andreas Christensen and Marcus Rashford scored late for Barcelona in a 2-0 win over third-tier Guadalajara.