The veteran striker swapped St Mary’s for Anfield over the summer alongside Adam Lallana and Dejan Lovren, which led to claims that the Saints may struggle this term – manager Mauricio Pochettino and young full-backs Calum Chambers and Luke Shaw also departed.
However, new boss Ronald Koeman worked well in the transfer market to land Graziano Pelle and Dusan Tadic, and Southampton currently occupy fourth spot with 13 games remaining.
Liverpool have turned around their poor form since the start of 2015 and are now back on course for a top four finish, making Sunday’s game with the South Coast outfit a ‘six pointer’.
And Lambert thinks that his former side are genuine candidates who could take one of the sought after positions away from them:
“I can’t say I saw the season they’ve had coming,” he told the Liverpool Echo.
“But when I look back now, not only myself but I think a lot of people under-estimated the characters in the dressing room who stayed there. That’s full credit to them for proving everyone wrong.
“They’ve done it year in, year out there and now they’ve taken it to another level. Ronald Koeman looks like a good manager and the new signings have come in and hit the ground running. The journey that club has been on has been amazing.
“The fact they’re still up there at this stage means without a doubt they are genuine top four contenders. Nothing seems to be fazing them.
“Even when they aren’t playing so well they grind out results. Defensively, they are very solid. Their new attacking players have come in and done really well. It’s going to be a hard game for us.”