Paul Drinkhall took the first set in the opening match against Marcos Freitas but the Portuguese player fought back to win 3-1.
And 19-year-old Liam Pitchford also took the lead in his tie before Joao Monteiro turned things around to claim a 3-1 victory and put Portugal 2-0 ahead.
Pair Pitchford and Andrew Baggaley slipped to a 3-0 loss against Monteiro and Tiago Apolonia as they failed to mount a comeback, giving Portugal a comfortable victory overall.
Despite their exit, Baggaley was pleased with his performance and remained upbeat about his future in the sport.
“I'm going to be a danger man in Europe over the next five or six years,” he said. “I feel I'm playing really well and I'm looking forward to my first season in the German Bundesliga."
And Drinkhall – partner of fellow Team GB table tennis player Joanna Paker – declared the strength and experience of their opponents as too much to overcome.
“They've been performing at this level for a long time. They're experienced. We're still a young team and we really pushed them,” said Drinkhall.
“One or two points the other way could have turned the match. We need to make less unforced errors to win at this level."
Elsewhere, Germany dumped Sweden out to again lead Europe's attempt to break Asia's increasing dominance in the sport.
Germany, silver medallists behind China in Beijing four years ago, came from behind to triumph 3-1 in the battle between Europe's two most successful table tennis countries.
Victory was sealed by Bastian Steger, Germany's third-ranked player, who defeated Jorgen Persson in the veteran Swede's seventh, and final, Olympic Games.
The three top seeded men's teams - China, South Korea and Japan - play their first round matches on Saturday, and German coach Jorg Rosskopf was unhappy that his team had to play the day after the singles event finished.
"I was very scared because I knew it would be tough for my players to change from singles to the team event," Rosskopf said, praising the fightback. "It was a success for the whole team."
Sweden (3) and Germany (4) have each won Olympic men's medals since the sport was introduced in 1988, behind only China (19) and South Korea (9), the first and second seeds who respectively play Russia and North Korea on Saturday.
- Andrew Baggaley