United fizzled out in the second half and Norwich looked more likely to break the deadlock as David De Gea kept out a Teemu Pukki shot from the edge of the area before Ronaldo struck, sending Krul the wrong way.
Cristiano Ronaldo converted a 75th-minute penalty to give Manchester United a barely deserved 1-0 win at Norwich City in the Premier League on Saturday after the visitors struggled to create chances at Carrow Road.
The result lifted United to fifth place in the standings on 27 points from 16 games, behind fourth-placed West Ham United on goal difference, while Norwich stayed bottom on 10 points.
United's interim boss Ralf Rangnick was pleased with the outcome and a solid defensive performance but conceded that they needed to improve in every department.
"From the start we controlled the game but didn’t always have the best possible solutions," Rangnick told the BBC.
"It's another clean sheet but still a lot of work to do.
"The second half I was not at all happy with the amount of corners that we gave away, but we got the three points.
"Now we have two clean sheets which is good but we still need to improve on that away, especially against physical teams or teams that attack high like Norwich did. They didn’t play like a bottom team."
Ragnick's counterpart Dean Smith was pleased with Norwich's fighting spirit and contested referee Darren England's decision to award United the penalty.
"We’ve just played two of the top six, we dominated at Tottenham but didn’t take our chances and we’ve gone toe-to-toe today with one of the big guns and a dubious penalty won it for them," he said.
United lacked a cutting edge until Ronaldo drove in the spot-kick after he was hauled down by home defender Max Aarons.
Ronaldo saw a shot beaten away by Tim Krul in the 37th minute and the home goalkeeper also tipped over a Harry Maguire header on the stroke of halftime after Alex Telles had hit the bar with a deflected free kick early on.
United fizzled out in the second half and Norwich looked more likely to break the deadlock as David De Gea kept out a Teemu Pukki shot from the edge of the area before Ronaldo struck, sending Krul the wrong way.
The home side piled on pressure in the closing stages and De Gea rescued United again when he clawed out an Ozan Kabak header before Eric Bailly deflected a Billy Gilmour shot with a last-gasp lunge.
United captain Harry Maguire praised De Gea and acknowledged United were not at their best, saying they needed consistency in grinding out results.
"David De Gea did great today," the central defender told Sky Sports. "We’ve been very disappointed with our defensive record this year, we know we need to do better.
"When you're playing every week, some performances aren’t going to be at the highest level. You see the top teams do it, they don’t play well every week but they still get the result."
