Tottenham boss Nuno Espirito Santo said the club's "feelgood factor disappeared" as they were beaten by Pacos de Ferreira in the Europa Conference League play-off first leg.
He left the entire starting XI from Sunday's 1-0 win over Manchester City - and Harry Kane - at home.
They were very poor in Portugal.
Lucas Silva ran in behind Cristian Romero too easily to latch on to Nuno Santos' through ball and slot into the bottom corner for the only goal.
"Nobody likes to lose a game," said Nuno. "Nobody likes to not play good. The feelgood factor disappeared. This is football, ups and downs. The players have to bounce back."
Spurs did not manage a single shot on target - but Nuno said he did not underestimate the hosts and would pick the same team again.
"The decision was to try to give minutes to players, to get minutes on their legs and increase the levels of fitness," he said. "Of course things take some time.
"I would decide the same. We need all the players [this season]."
Their European campaign - in the new third-tier tournament - will be over in August unless they win next Thursday's second leg at Tottenham Hotspur Stadium.
Nuno started three summer signings - defender Romero, winger Bryan Gil and goalkeeper Pierluigi Gollini.
Teenagers Nile John and Dane Scarlett also made their first starts for the club - and J'Neil Bennett and Maksim Paskotsi came on for debuts - but there were no real standout performances.
Identical twins Michael and Matthew Craig, 18, were among the unused substitutes on an inexperienced bench.
Nuno would not say if he will play a similar team for the second leg, adding he wanted to focus on Sunday's Premier League game with former club Wolves first.
Paços de Ferreira
- 13Magalhães Ribeiro Ferreira
- 29Ferreira Fonseca
- 32da Silva Ramos
- 2Costa Baixinho
- 5Pacheco AntunesBooked at 66mins
- 22Martins Moreira
- 7Castro FerreiraBooked at 34minsSubstituted forSilva de Jesusat 72'minutes
- 77Valente SantosSubstituted forBobó Djalóat 62'minutes
- 23da Silva de JesusSubstituted forDelgadoat 72'minutesBooked at 74mins
- 10Pereira JuniorSubstituted forSousa Silvaat 88'minutes
- 3Reis Lima
- 9Silva de Jesus
- 12Menezes de Almeida
- 16Bobó Djaló
- 20Alves Bastos
- 21dos Santos Silva
- 25Ferreira de Oliveira
- 26Guerra Pires
- 45Sousa Silva
- 99Da Silva Souza
- 38Carter-VickersSubstituted forPaskotsiat 87'minutes
- 33DaviesBooked at 31mins
- 18Lo Celso
- 19R SessegnonSubstituted forBennettat 81'minutes
- 43JohnSubstituted forClarkeat 45'minutes
- 11GilBooked at 90mins
- Maurizio Mariani
- Shots on Target
- Our coverage of Tottenham Hotspur is bigger and better than ever before - here's everything you need to know to make sure you never miss a moment
- Everything Spurs - go straight to all the best content