But after the drama of the shootout dissipated, attention quickly turned to Italy's captain Chiellini whose strange antics before penalties won over fans on social media.
Both sides failed to convert their opening spot kicks as Manuel Locatelli's effort was saved and Dani Olmo blasted over the bar. Italy nailed its next three penalties while Spain slotted home twice, before Alvaro Morata's shot was saved.
Italy scored its fifth penalty, courtesy of Jorginho, to secure victory, with a 4-2 scoreline in the shootout.
Morata's late equaliser saw Spain force extra time at Wembley this morning as the contest stood deadlocked at 1-1 after 90 minutes.
Federico Chiesa gave Italy the lead with a fine curling strike on the hour mark. But the much-maligned Morata, dropped to the bench for the first time in the tournament, was introduced as a substitute and slotted home with 10 minutes remaining after a neat one-two with Olmo.
Italy will face England or Denmark, who play on Thursday morning, in Sunday's final in London.
Penalty shootouts are incredibly stressful affairs but Italy captain Chiellini managed to remain calm. Footage of him smiling and enthusiastically embracing Spanish skipper Jordi Alba before the shootout started immediately went viral, the internet absolutely losing it over Chiellini's antics amid confusion at the coin toss about which goal the shootout would take place at.
Sports writer Pat McCarry tweeted: "Chiellini forever has my heart after this."
Darren Cleary said it was "more proof that Chiellini is the greatest footballer that ever lived" while podcaster Roger Bennett said: "Humanly incredible: Under the crucible of pressure ahead of a penalty shootout, Giorgio Chiellini is just a boss. A 36-year old who still loves the game of football with as much passion as when he was a tiny kid."
Sabreena Merchant added: "Would love to be as joyous as Giorgio Chiellini before something as stomach-churning as penalties."
Zac Pacleb tweeted: "Chiellini is absolutely the guy who sees you show up at the party and yells 'ayeeee there he is!!! party is here!!!!' and then gets you properly hammered."
Spain was the better side for long spells of an epic contest before Chiesa gave Italy the lead in front of almost 58,000 spectators.
Morata, who was dropped from the starting line-up here, came off the bench to equalise with 10 minutes of normal time left.
Spain, who had beaten Switzerland in a shoot-out in the quarter-finals, had also beaten Italy on penalties at Euro 2008, but this time misses from Olmo and then Morata saw them stumble out of the tournament.
The Italians celebrated at the end with a large contingent of their UK-based supporters, and a team that has been rejuvenated under Roberto Mancini continues to dream of winning a first European Championship title since 1968.
It is nine years since Spain mauled Italy 4-0 in the Euro 2012 final in Kiev to win a third consecutive major tournament, and this was the fourth consecutive European Championship in which these powerhouses had met.
The football was absorbing and of the very highest quality, particularly in midfield where Italy's outstanding trio of Jorginho, Marco Verratti and Nicolo Barella met their match in Spain's Sergio Busquets, Koke and Pedri.
Giorgio Chiellini of Italy interacts with Jordi Alba of Spain before the penalty shootout. Photo / Getty
The latter, just 18, is a frightening talent and his touch and calmness on the ball indicate he will be Spain's leader for many years to come.
What the game lacked in the first half was drama in front of goal, although Italy's Gianluigi Donnarumma made one crucial save to deny Olmo in the 25th minute. Italy missed Leonardo Spinazzola, their outstanding left-back who suffered a torn Achilles tendon against Belgium in the quarter-finals.
Meanwhile Spain coach Luis Enrique dropped Morata and selected Mikel Oyarzabal to start on their right flank up front.
Spain had enjoyed the better of the game but Italy went ahead on the hour thanks to a goal of the highest quality. A move that started with Donnarumma's throw saw Lorenzo Insigne play Ciro Immobile in behind.
Immobile was thwarted by Aymeric Laporte's tackle but the ball fell to Chiesa and he picked his spot in the far corner of Unai Simon's goal on his right foot. The Italian fans, gathered en masse at that end of Wembley, erupted in celebration.
Spain reacted by sending on Morata and Gerard Moreno, and just as Italy looked to be seeing out the victory, Morata was the man who got the leveller.
