Cristiano Ronaldo's Portugal beat the Czech Republic 2-1 to claim a Euro 2024 debut victory on Tuesday but they needed to come from behind with a 92nd-minute winner from youngster Francisco Conceicao.
Earlier in the section's other clash, Turkey bested Georgia 3-1 in a pulsating match in Dortmund.
Roberto Martinez's Portugal qualified at a canter with a 100 percent record, but only just scraped victory in Leipzig in their first match, under driving rain.
Ronaldo played at a record-extending sixth European Championship and 41-year-old defender Pepe became the tournament's oldest ever player for the Selecao.
The Czechs went ahead against the run of play through Lukas Provod's fine strike from the edge of the box after the hour mark, but Robin Hranac's own goal soon pulled Portugal level before Conceicao's winner.
"We want to do more, but there was also a lot of emotion, a lot of desire and sometimes we failed to pull off the strategic plan," said Portugal midfielder Vitinha, awarded player of the match.
"We wanted to come out strong, show our strength and unfortunately we conceded the goal first, on the Czech Republic's first opportunity.
"We showed all our coolness and resilience."
Portugal supporters chanted Ronaldo's name and imitated his "Suuuui" celebration shout as they marched to the game waving flags and in high spirits despite a brief but intense thunderstorm.
Around 8,000 fans attended Portugal's open training session on Saturday, many of whom were just hoping for a glimpse of the 39-year-old former Real Madrid striker.
Thousands of fans sported replica Ronaldo shirts but were unable to watch the all-time record Euros goalscorer find the net on a frustrating night against a solid Czech side.
Ronaldo was thrice denied by goalkeeper Jindrich Stanek on a record Euros appearance and headed against the post, but was offside.
Diogo Jota put the rebound into the net but the goal was disallowed after VAR highlighted Al Nassr striker Ronaldo's infringement.
It did not matter for Portugal in the end as 21-year-old Porto winger Conceicao struck from close range.
"We have a great team spirit, we will fight until the end and Portugal will be alive until the end," said defender Mendes.
The Czechs were left agonising after battling so hard and almost claiming a point.
"It hurts terribly when you work like this for 90 minutes, you give everything and you lose in the end," said Czech goalscorer Provod.
"Our defenders played an incredible game. We just needed a bit more luck."
Turkey turn-out
A well-supported Turkey started the Euros in entertaining fashion with an end-to-end win over debutants Georgia.
Real Madrid playmaker Arda Guler scored a brilliant goal, along with strikes by Mert Muldur and Kerem Akturkoglu, to delight the masses of Turkish supporters.
Georgia were dangerous after Georges Mikautadze levelled Muldur's superbly hit opener, and struck the woodwork.
Napoli star Khvicha Kvaratskhelia was below his best but despite defeat his team offered enough to give themselves hope for the matches ahead, against the Czech Republic and then Portugal.
"It was a match worthy of the Euros, we had great support even in difficult moments. This win is also for them and the party that they'll have," Turkey coach Vincenzo Montella told reporters.
"It's my 50th birthday today so it was perfect day of sport and the victory was the best present that the boys could have given me."
Hosts Germany are back in action on Wednesday as the second round of group matches commences, facing Hungary in Stuttgart.
Scotland are chasing their first victory at a major tournament since 1996 as they take on Switzerland in the other Group A match, while in Group B Croatia play Albania.
