Klopp changed all of his outfield players at the half-time break and two of the youngsters introduced went on to play a starring role.
Bilbao, meanwhile, have already begun their campaign for the 2017/18 season, with the Europa League qualifiers underway.
Fans were waiting outside the Marker Hotel in Dublin's Docklands for a chance to meet their heroes before the game.
Record signing Mohamed Salah and Sadio Mane used their speed and trickery to terrorise the Bayern defence and both finished the game on the scoresheet.
There is renewed interest from Barcelona in the Brazilian ace with some reports claiming they are preparing a £108m offer for the attacking midfielder but Liverpool remain adamant they want to keep him.
- Dominic King (@DominicKing_DM) August 5, 2017Dom Solanke is what #LFC hoped Andy Carroll and Chris Benteke would be.
He will also be a major doubt for England's next two World Cup qualifiers, against Malta and Slovakia in September. With Coutinho's money pocketed, the Reds could comfortably pay the inflated asking price and bring the Dutchman to Anfield.
But the Liga side levelled only nine minutes later through Williams after the rebound off Dejan Lovren's slide tackle put the 23-year-old forward in front of goal.
He added: "We've had a lot of games in pre-season and we didn't lose one".
Athletic Bilbao has won four, drawn one and lost one of their six previous pre-season friendlies.
At least we won't have to play on a plastic pitch in Switzerland. With Jose Angel Ziganda likely to start with a largely second string side, the Reds definitely have the edge. Liverpool appear to be facing an injury crisis at the worst time possible - with the Premier League set to begin in just over a week. The Hard Tackle predicts a 3-1 win for Liverpool.