'Scary' Portugal flex strength in depth to avoid slow Euros start
Two substitutes combined for a 92nd-minute winner as Francisco Conceicao struck his first international goal with his first touch of the ball from Pedro Neto's cross.
Another of those sent on by coach Roberto Martinez on Tuesday in Leipzig had also found the net, but Diogo Jota's header was ruled out for offside against Cristiano Ronaldo.
Portugal followed the path of England and France as all three of the pre-tournament favourites got off to winning starts, albeit in unconvincing fashion.
Ronaldo was as ever the focus of attention, but the Portugal captain endured a frustrating night. He will have to wait to add becoming the European Championship's oldest goalscorer to his collection of records.
Martinez's decision to stick by the 39-year-old as the focal point of his attack may come under closer inspection as the tournament progresses.
Ronaldo was dropped for Portugal's final two matches at the 2022 World Cup and replaced by Goncalo Ramos.
The Paris Saint-Germain striker Ramos this time never got off the bench, along with Barcelona's Joao Felix, to underscore the wealth of attacking talent on offer to Martinez.
"We are a country of 10 million but we have a huge amount of players in the (European) top-five leagues," said Martinez.
"That's a strength and a weakness. If you don't use it well, it can become 26 individuals trying to show their own thing."
'Ultimate example'
The Spaniard Martinez has plenty of experience of major tournament football.
He took Belgium's so-called golden generation to the World Cup semi-finals and Euro quarters, but this is his first shot at glory with Portugal.
Many have questioned whether the former Wigan and Everton manager is the right man to summon the best from such an abundance of talent.
The critics would have been ready to pounce as Martinez waited until the 89th minute to introduce Conceicao and Neto as part of a late triple change.
But on a night when Pepe became the oldest player in Euros history at 41, and Ronaldo also passed the previous mark for an outfield player, it was Portugal's new generation that got them out of trouble.
Twenty-four years on from when his father Sergio scored a hat-trick against Germany at Euro 2000, Conceicao enjoyed his breakthrough moment for his country on German soil.
Conceicao senior has also been his son's manager at Porto for the majority of Francisco's club career.
Martinez, though, said the 21-year-old winger had proved he was worthy of standing on his own two feet.
"He is the ultimate example of earning it. He showed he is ready," added Martinez.
"Francisco is a very mature player. He plays vertically and he's got a nose for danger in the box.
"For a national team coach, having a player like that is great."
Unlike England and France, who were 1-0 winners over Serbia and Austria respectively, Portugal were forced to come from behind after Lukas Provod put the Czechs ahead against the run of play.
Robin Hranac's own goal quickly levelled and Martinez hopes the character showed by Portugal will make a "scary" collection of stars even harder to stop over the next month.
"Things were tough for us today, but the way the team reacted, it is great for a coach to have a group of players as resilient and scary as they are."