The 25-year-old popped up in the 80th minute to seal a 2-1 victory for the Premier League side over Trencin of Slovakia on Thursday.
A goalless first leg left Bruce's side needing to win in front of a packed KC Stadium, but visiting goalkeeper Milos Volesak was in fine form to routinely deny the hosts.
However, after seeing Aluko pounce on Robert Snodgrass' knock-back to seal a first European victory for Hull, Bruce believes the forward is back to his best after an injury-hit 2013-14.
Bruce said: "Sone, touch wood, has looked the best I've seen him in seven years, physically.
"He pulled up in training a couple of days ago - he was a little bit stiff with all the work he's done. I'm delighted for him he's been able to score a goal.
"We all know, the people of Hull, he's got terrific ability so let's hope he stays injury-free because he's going to be a big player if he does.
"I honestly believe that the ability to bring people off the bench is what won us the game.
"That's the squad, that's why we want the squad the way we have.
"When you can bring on the likes of Aluko and (Tom) Ince in particular, that gave us a freshness and changed the game."
Having seen his side pass up a number of chances to take the lead after Ahmed Elmohamady had cancelled out Tomas Malec's early opener, Bruce conceded he had wondered if it was to be Hull's day.
"Usually playing in Europe you don't get that many [chances]," he explained. "And to be fair we've missed three or four glorious chances and you think 'Are we going to get it?'
"As always we stuck at it after an awful start that put everybody on edge for 20-25 minutes, including the players and the crowd, who I thought were fantastic.
"There was a frustration there but thankfully we've seen it through."
