Gareth Southgate was frustrated by England Under-21s' performance against Finland despite running out 3-0 winners.
Saido Berahino struck twice after Michael Keane opened the scoring as the Young Lions won their Euro 2015 qualifier by a comfortable margin in Milton Keynes.
The result moves England three points clear of the top of Group 1, but the manner of victory was not up to the standards of recent displays.
After going in at half-time with a two-goal cushion, Southgate's side were poor until Patrick O'Shaughnessy was sent off the visitors with 20 minutes remaining.
"I am pleased with the result," the Young Lions manager said.
"I think we have got to be careful because they are young players and have done really, really well in the period of time we have been working together.
"But we have set ourselves a standard and I didn't think we quite achieved that tonight.
"We won't always hit the heights we did in the last couple of games and I think we played an opponent intent on frustrating.
"When we got clear, several times they made fouls which broke things up, so it is probably not a bad thing that we have had a performance where we can improve a lot on it, despite winning and sitting top of the group."
Southgate's side will look to make amends on Tuesday evening against minnows San Marino in Shrewsbury - a game Thursday's man of the match Berahino will miss.
After scoring his first of the night, the in-form 20-year-old paid tribute to his father by showing a shirt with 'RIP Love U Dad' scrawled on it.
Berahino's father was one of the estimated 300,000 killed in the civil war that plagued his homeland of Burundi and the gesture led to the striker being rather harshly booked, incurring a suspension.
"He is a good player, a good finisher and a pleasure to work with," Southgate said of West Brom front man.
"He has got a desire to improve all the time and he is a terrific goal threat for us.
"That said, looking at our bench tonight we have some super players I didn't put in the starting line-up that I think can cause a lot of problems.
"I hadn't realised he had been booked until he came and apologised at half-time. I couldn't quite work out what he was apologising for.
"The rules are what they are and again that is something we've got to learn. Hopefully it won't be too costly for us.
"I think it was a personal thing that he had done it for, but had I have known I would not have let him go out there with that on his shirt."