Under-23s manager Neil Thompson believes there is still plenty of room for improvement despite the Owls' hard-fought victory over Millwall.
Joe West's first half header ensured Wednesday kicked off the new Professional Development League Two North campaign with a win at Middlewood Road yesterday.
Wing back West headed home Jack Stobbs' superb delivery in the 21st minute to settle a hard-fought encounter.
Thompson told The Star: "I thought we played really well in the first half. We had a lot of the ball and scored a really good goal.
"Jack [Stobbs] got in down the right and it was a good finish from Joe [West].
"We could have maybe been a little more clinical in the final third.
“I thought we controlled the game and then we came out for the second half and, for some reason, were really sloppy for 15 to 25 minutes.
“We didn’t play with enough energy and then we wrestled the game back although they (Millwall) didn't create a load of chances.
“Then I thought the last ten or 15 minutes, when we changed the system, we looked a little bit better and could have added to it.
"I think we deserved the win but there was that middle bit of the game just after half time which we need to be better at."
Stobbs stood out in a first half which Wednesday largely controlled. His direct style of play frequently troubled Millwall's defence, although his crossing was always perfect.
"Jack got in some great positions and he knows it," said Thompson. "He just has to be a little more clinical."
The Owls, watched on by first-team manager Jos Luhukay, were second best in the early stages after half-time.
Millwall should have made them pay but striker Kushal Campbell-Palmer fluffed his lines in front of goal after latching on to Reuben Duncan's pass.
Thompson was baffled by their slow start to the second half.
"The heat got up; it was the lads’ first game of the season but they have done their work and I think it showed in the legs because in the last 15 minutes we had a lot more energy," said Thompson.
“Just sometimes it happens like that. We had quite a few young lads playing against Millwall. A few missing from our normal group.
“Isaac Rice played 90 minutes with the Under-18s and he come in and did a great job."
Wednesday: McCulloch; Brennan (Waldock 56), Williams (Dawodu 79), Rice; Hughes, Lee, Kirby, West; Stobbs, Lonchar, Borukov. Substitutes: Wallis, O'Brien, Ellery.
Millwall: Sandford, McNamara, Wicks, Hanson, Parker, Stojsavljevic, Harvey (Davies 88), Skeffington (Mitchell 63), Campbell-Palmer, Duncan, Saunders-Henry. Substitutes: Mitchell, Wright.
Referee: Mr D.McNamara.