It had been difficult to locate much optimism in Dublin beforehand about the Republic of Ireland's chances against the second-best team in world football. Never mind the chastening experiences of the Euro 2012 finals, when Giovanni Trapattoni's squad departed Poland battered and bowed, their World Cup qualification campaign had begun with them dodging a bullet in Kazakhstan. The late 2-1 victory was hugely fortuitous.

There was no escape here in what represented a new low for the under-pressure Trapattoni. All of the pre-match fears were realised in brutal fashion as Germany, despite a slow start, purred through the gears to visit humiliation on Ireland. Marco Reus was the destroyer in chief, his first-half goals ending the game as a contest and begging the question that had always felt central to the occasion: by how many would Germany prevail?

The second-half came to resemble a training exercise. The outstanding Mesut Ozil, Miroslav Klose and the substitute Toni Kroos got the goals – Kroos' pair were rattled in from distance – and it was a dismal experience for everyone connected to the Irish set-up. The minutes ticked like hours and the atmosphere, which had been vibrant at the start, when Ireland actually looked compact and committed, turned sour.

It was the scale of the capitulation that was most worrying and Trapattoni has work to do to lift morale before Tuesday's tie in the Faroe Islands. It feels as if his job will be on the line. The Italian has shaped his Irish adventure upon defensive resilience but there was nothing here after the half hour, Germany cutting through them almost at will. Trapattoni's team have now conceded 16 times in five competitive ties and this was the heaviest home defeat in Irish football history. The substitute Andy Keogh's injury-time goal was the most hollow of consolations.

Jon Walters, who started as the lone striker in a new-look Trapattoni formation, was perhaps the solitary positive and he caught the mood when he described the performance as "embarrassing".

"We let ourselves down, the manager down and we let the country down," he said. "We can't be anything but apologetic."

Trapattoni remained defiant, insisting his players would pick themselves up. He dismissed the suggestion that his time in the job was up; that he had run out of ideas to motivate the players. He said that he would fight on because he was "proud".

It was ominous, though, that he spent a significant portion of his post-match briefing talking up his achievements in qualifying for Euro 2012 and, also, the very near miss at the 2010 World Cup. He reminded his audience of Ireland's state when he took over in 2008 and the amount of players he had developed. Nobody is criticising what he did up to the European Championship. It is what happened at them and since that is of deep concern. The future is fraught.

Trapattoni had been forced to make sweeping changes as Ireland started for the first time in 15 years without Shay Given, Damien Duff, Richard Dunne or Robbie Keane. The first two have retired; the other two injured. With problems elsewhere, Trapattoni named only four players from the line-up that had started the final group tie of the failed Euro 2012 campaign against Italy. He prizes experience and continuity. The upheaval and lack of established international alternatives made him nervous.

Joachim Löw, the Germany manager, could afford to start Kroos and Lukas Podolski on the substitutes' bench and omit Mario Götze entirely. His team dictated the tempo and although they did not threaten until past the 30 minute mark, when they did, the tie turned sharply.

Ireland's defensive concentration lapsed in shocking fashion when John O'Shea lost possession to Reus and then seemed to drag down the winger inside the penalty area. Surprisingly, the referee, Nicola Rizzoli, booked Reus for diving. The German had has his revenge in the next attack. Bastian Schweinsteiger's floated ball invited Marcel Schmelzer to maraud into the box and, when the ball broke, Reus shot high into the net.

Germany's second brimmed with quality. They played the ball out from the back, under pressure and, once Ozil had dipped his shoulder and glided away from James McCarthy, the alarm bells sounded loudly. Ozil moved possession to the right-back Jérôme Boateng, he played it across the field for the advancing Reus and his low left-footed drive billowed the far corner of the net.

Trapattoni made an attacking change in the 51st minute, bringing on Shane Long for Keith Fahey but the home crowd's mood was killed shortly afterwards when Darren O'Dea, already on a yellow card, cut recklessly through Klose inside the area. Ozil's penalty was ice-cool.

Klose's goal came after he rounded Keiren Westwood and threaded home from a seemingly impossible angle while Kroos's shooting oozed power and conviction. His first, a vicious left-footed volley, was the goal of the tie but his second ran it close. Trapattoni could only admit to his team's "inferiority."

"Usually, we are more aggressive," he said. "But after 30 minutes, we were without strength or energy. We had no direction."

The fear is that Trapattoni will not rediscover it.