Harry Wilson and Rhian Brewster scored for the European champions but goals from Paco Alcacer, Thomas Delaney and Jacob Bruun Larsen were enough for Dortmund to take a deserved 3-2 win at the University of Notre Dame.
The game was played in stifling temperatures of 33C – in a ground hosting its first football match.
Just two of the side who started the Champions League final played for the first hour against a strong Dortmund XI, but Klopp tried to take positives from the first game of a three-match trip to the US.
“You could see that Dortmund are a step further in their preparations but there was a lot of good things for us as well,” he said.
“How we conceded goals was a lack of organisation, but it is very difficult to have that at this stage.
“Really I learned nothing. But it is difficult when the ball isn’t rolling. It was a tough night for both teams – it was really warm.
“I don’t like what I see in a game in pre-season very often but there is always a reason for it. I am not over the moon with our performance but I know there is lots to come.”
Wilson pick of the bunch
Without them – and the injured Xherdan Shaqiri – Klopp started last season’s cameo hero Divock Origi flanked by Harry Wilson and Ryan Kent, who both shone on loan last season.
Wilson, 22, scored 18 times while playing under Frank Lampard at Derby and will probably be back out on loan again by the time the transfer window closes, but showed calm in front of goal when he ran on to Fabinho’s excellent pass to equalise.
Kent helped make the goal with a fine dummy, but should already have scored when his shot was well saved by Marwin Hitz.
Brewster, 19, was one of 10 planned changes on the hour mark and scored his fourth goal of pre-season with an emphatic penalty late on.
Soft goals in South Bend
A second-string Liverpool defence looking understandably rusty at times as they conceded goals early in each half.
Nathaniel Clyne’s very pre-season attempt to clear a third-minute cross allowed Alcacer to smash the opener past Simon Mignolet, and Dortmund – who made nine changes at half-time – then scored two quick goals after the restart.
New signing Thorgan Hazard crossed for Delaney to tap in after a corner was not dealt with, and Larsen then finished sharply from a Marius Wolf cross after teenage left-back Yasser Larouci was caught on the ball.
Other than that academy product Larouci, born in Algeria but also qualified to play for France, was sharp enough, with Klopp praising him for dealing with “one of the biggest talents in world football” in the shape of the largely anonymous English forward Jadon Sancho during the first half.
Reds light up red-hot Indiana
That had not stopped the bulk of a 40,361 crowd from turning up four hours before kick-off to ‘tailgate’ – loudly sing, eat and drink in the car parks outside the impressive Notre Dame Stadium.
The ground was just over half full, but those who had shelled out between $50 and $600 (£40-£480) for a ticket – and another $60 to park the car – made plenty of noise throughout what one fan told me was “the biggest thing to hit town since Garth Brooks”.
Liverpool: Mignolet, Clyne (Alexander-Arnold), Matip (Lovren), Gomez (Van Dijk), Larouci (Robertson), Fabinho (Henderson), Milner (Wijnaldum), Oxlade-Chamberlain (LeWIS), Wilson (Jones), Kent (Woodburn), Origi (Brewster).
Dortmund: Hitz, Piszczek (Morey), Toprak (Balerdi), Hummels (Pherai), Guerreiro (Schulz), Weigl (Witsel), Reyna (Bruun Larsen), Brandt (Delaney), Sancho (Reus), Gotze (Wolf), Alcacer (Hazard)
Subs: Delaney, Reus, Schulz, Balerdi, Philipp, Morey, Hazard, Wolf, Witsel, Bruun Larsen, Pherai, Oelschlagel