The 32-year-old striker follows in the footsteps of the likes of Robbie Fowler, Fernando Torres and Ian Rush in wearing the iconic shirt, which he donned for the first time in the 2-1 pre-season friendly win at Preston North End.
It was a moment to savour for the life-long Liverpool fan and local lad Lambert.
"I've always seen myself as a number nine as it's the type of player I am, and to get it at Liverpool is unbelievable," the close-season signing from Southampton told Liverpool's official website.
"I would have been happy with any number because as long as that badge is on the front I would have been happy with any shirt, but to get number nine is special for me."
Goals from Suso and Kristoffer Peterson in the space of three second-half minutes changed for the game for Liverpool at Deepdale following Josh Brownhill's opener.
Lambert played the first half in his first game since representing England at the FIFA World Cup.
On his Liverpool debut, he added: "It was special.
"I had to get a few moments in check at the beginning, but it was special.
"Obviously I'm professional, I'm 32 now and I'm able to get my emotions in check, and now it's all about my fitness.
"That's all I was concentrating on, trying my best and trying to get a goal. I was a little bit disappointed not to get a goal but I thoroughly enjoyed it.
"I was nervous before kick-off and I probably haven't been that nervous for a while.
"I've played in a lot of big games in my career and that's the most nervous I've been before a game for a while, but it was a special moment for me and one I'll remember."
