James Hayter had fired Rovers ahead just before half-time when racing on to Dean Shiels' precision pass to slide the ball under Blades goalkeeper Mark Bunn.
Doncaster celebrated their first ever league win at Bramall Lane in January, but had to settle for an eighth draw from their opening 11 league matches ahead of next week's international break.
Blackwell insisted his side dominated the match, but conceded they were struggling to find their better form due to the number of loan signings he has been forced to make.
Cresswell, Glen Little and Jordan Stewart all made their full home league debuts.
Blackwell said: "Overall I can't complain. We've done most of the things we asked.
"The debutants all did well. I think we've signed 12 or 13 players now and at times we do look a bit disjointed, but we dominated and they didn't pose us many problems."
He added: "The lads are showing character in abundance, but the team's being rebuilt again. This is the third team I've built since being here and I've only been here 18 months.
"After Christmas we signed five or six loans and this year I've got 12 new players in and six are loans.
"The understanding of what I want isn't quite there, but we're still getting results.
"So I'm pleased with that. We're sitting sixth after 11 games so that school report is 'doing okay, but could do better'."
Blackwell confirmed Nick Montgomery and James Harper were nursing knee injuries and Jamie Ward had required surgery earlier in the week on a fractured wrist.
Rovers manager Sean O'Driscoll, who agreed not to play Blades striker Billy Sharp despite there being no clause in the loan agreement, could be ready to draft in some new faces following the latest spate of injuries to hit his squad.
Skipper Brian Stock is out long-term with a knee injury, stand-in captain Adam Lockwood missed out and will be sidelined for up to three months after breaking a bone in his foot, James Coppinger is struggling with an ongoing calf strain and Mark Wilson limped out of the action with a similar problem.
O'Driscoll said: "Every manager in the Football League wants to add to his pool, but whether you can get the quality you want or afford what you want.
"We're a team with average gates of 8,000 so we're not going to spend millions of pounds on new players. I wish we could, but we can't.
"But it could be imperative now I've got one or two more injuries. The (international) break's come for us, so we'll get a clearer picture of where we are.
"Ideally we'd love to, but whether it's possible I'm not sure."
O'Driscoll had special praise for defender Byron Webster, who required a pain-killing injection to get through his full league debut after hyper-extending his elbow in the first half.
O'Driscoll added: "He didn't want to come off and that augurs well for his future.
"He did well. He's going to be one of those centre-halves who's not a header or a kicker, he's going to be a cultured defender. He's got vast potential."