Thursday's third round qualifier against Vitesse Arnhem will be Saints' first on the continental stage since 2003 - a period in which they have plummeted to the third tier and verge of liquidation, only to rise again and last season achieve their best ever Premier League finish.
That brought with it European qualification for just the seventh time in the club's history, pitting Koeman against the club with whom he cut his managerial teeth.
The Dutch great coached Vitesse Arnhem at the turn of the millennium and believes his current side can triumph in their third qualifying round tie.
"We know to reach the group stage we have to win two qualification rounds and it's all about what we did last season," Koeman said.
"We are looking forward, it's for everybody - the fans, the club, the players.
"We are ready
It's still not the start of the Premier League but the boys are in a good shape, physical way, strong.
"We saw in Holland last week what we can expect of the opponent and we are ready for the challenge, because we see it as a challenge to play in Europe."
The two-legged clash against Vitesse is a far cry from heading to Carlisle, Hartlepool and Dagenham and Redbridge not so long ago.
Jose Fonte was part of the side promoted from League One and remains an integral member four years on, making Thursday's first leg particularly sweet for the Portuguese.
"It's definitely one of the proudest moments in my career," Fonte said ahead of the sold-out St Mary's encounter.
"We have been together for a long time and through all the dark, tough years, and now to be leading the team hopefully tomorrow will be a very proud moment.
"I am extremely happy and want the game to come as soon as possible."
Koeman's side head into the clash buoyed by impressive pre-season showings against Dutch outfits, having put 10 past lower league side Quick '20 either side of 3-0 victories against Groningen and Feyenoord.
Those matches will no doubt help the Dutchman against former club Vitesse, while the results suggest the influx of new signings are gelling well.
Fonte has been impressed by the new boys and believes they are capable of filling the void left by Morgan Schneiderlin, Nathaniel Clyne and Toby Alderweireld.
"First, we didn't let as many players leave as last season which is very important," the Portugal international said, referring to last summer's talent drain.
"We lost quality players but the replacements were the same quality
We are in a good place, everybody knows each other.
"The new guys showed already they have a lot of quality so I am really relaxed on that aspect."
Source : PA