The 20-year-old scored the third-and-final goal in Saturday evening's win over the Turkish side at the Stadion Villach Lind in Austria.
The First Team will now return to England at the end of an 18-day stint in Spain then Austria, where Isgrove's performances in training and in matches have been a definite highlight.
Wales Under-21 international penned a new contract on the morning of Saints' departure for Spain, and he says he has enjoyed the level of progress he has been making of late.
"I've come a long way since Christmas," Isgrove told Saints Player
after Saturday's game. "I had injuries last year, but Radders (Senior Physiotherapist Matt Radcliffe) has helped me so I'm a lot stronger and fitter now.
"I'm playing games, which is all I've wanted to do since I came here. I was happy to sign the contract and to score a goal was a kind of reward for it.
"Obviously I'm really happy," he continued. "I've been working really hard towards a goal and waiting for one for a while.
"I've played four games in pre-season, and they weren't easy games. The first two were a bit different from the second two, where the opposition had international players – but that's good."
Saints trailed to Beşiktaş after 62 minutes, but goals from Rickie Lambert, Emmanuel Mayuka and Isgrove – all of whom were on as substitutes – earned Mauricio Pochettino's men victory.
Youngster Lloyd says the level of hard work the squad has been putting in behind the scenes contributed to the nature of the victory, adding that he will continue to put in maximum effort to ensure he stays in the manager's thoughts ahead of the new Barclays Premier League season.
"I think our fitness came through in the end," he affirmed. "They were obviously getting tired and it showed in the end.
"I've just got to keep working hard on the training ground and to keep getting match-time.
"Hopefully the gaffer keeps picking me, and I'll keep doing what I'm doing. I'll keep training and hoping for the game-time that I need to keep pushing on and into the team."