At half-time in east London, West Ham appeared well-placed to take control of their first European semi-final in 46 years, despite conceding after just 48 seconds.
They had responded impressively to another setback in this competition, Michail Antonio cancelling out Ansgar Knauff’s early goal, and shown enough to suggest they could overpower Eintracht in the second half.
Instead, it was the visitors who came on strongest after the interval and the Hammers ended the night relieved to still have a fighting chance in the tie, despite Jarrod Bowen twice striking the woodwork, including with a spectacular overhead kick in stoppage-time.
Moyes made six changes from the weekend’s defeat to Chelsea, including the surprise return of centre-half Kurt Zouma, but you nonetheless wondered if West Ham were beginning to pay for a campaign spent fighting on two fronts, as they laboured against their zippy Bundesliga opponents.
Moyes has made the fewest changes to his XI of any manager in the Premier League this season and is often reluctant to turn to his bench, demonstrated last night when he made just one change in Said Benramha, who also struck the woodwork with a fierce effort which skimmed off the upright.
The core of Moyes’ small squad is being pushed close to the limit, and Thursday night marked Declan Rice’s 50th appearance for club and country this season. For Tomas Soucek, it is 55, Pablo Fornals 53, Antonio 48, and Bowen and Craig Dawson 46.
Injuries have further increased the strain on key players, particularly at centre-half, and Zouma did not look at his imposing best after being rushed back from an ankle injury, despite making the equaliser in the 21st-minute.
The Frenchman rose to head Manuel Lanzini’s free-kick to the far post where Antonio got in front of Rice to hook home a deserved leveller.
Bowen had already struck the woodwork, his effort turned onto the post by the boot of goalkeeper Kevin Trapp, and at 1-1, with the London Stadium rocking again, West Ham had the platform to take control of the tie.
But there was evidence of tired legs among Moyes’ players, including for the Eintracht winner nine minutes after the break, when Soucek failed to track the darting run of Djibril Sow. He forced a save from Alphonse Areola, only for star-man Daichi Kamada to tap into the empty net.
Like the first goal, which burst the atmosphere within a minute, the winner was well worked but too easy for Eintracht, who were a constant threat on the counter-attack against a surprisingly flimsy Hammers side.
Kamada nearly made it 3-1 on the break while Rice was distracted by a spat with another Eintracht player, but his effort struck the post via a touch from Dawson.
In the final third, too, there were signs of fatigue and a missing spark. Bowen was West Ham’s standout player but lacked a final ball, more than once sending a sloppy pass too close to a defender.
Their set-pieces, usually such a strength, were particularly disappointing and Bowen, Lanzini and Aaron Cresswell all set efforts directly into the arms of Trapp, who quickly looked to spring a fresh counter.
Moyes’ side have shown impressive resilience so far in the knockouts and they should not be discounted, even against an opponent who saw off Barcelona in the quarter-finals.
West Ham trailed in the last-16 first leg but came back against favourites Sevilla, albeit with the second leg at home, before thrashing Lyon, despite losing Cresswell to a harsh red card early in the tie.
They are yet to go into an away leg trailing, however, so they will have to pull off their biggest comeback yet in what will be a ferociously loud and hostile atmosphere in Germany next Thursday.
Moyes is prioritising Europe over the Premier League and he can be expected to ring the changes again for Sunday’s visit of Arsenal — which should infuriate Tottenham — before demanding another big push from his players in Frankfurt.
This time last year, West Ham’s pursuit for a top four finish faltered and they limped over the finish line after injuries to key players derailed their final push.
Now, Champions League football is just two matches away but there appears a danger Moyes’ players could run out of steam again.