Though fears of a washout did not come to pass, the start was significantly delayed and only 30 overs were bowled, in which Labuschagne and Mitch Marsh combined for a 103-run partnership that kept alive Australia's hopes of grinding out a draw.
Play was abandoned after tea, with England left praying for the rain to stay away long enough on Sunday for them to ensure victory and take the five-match series into a decider at the Oval in London next week.
"Really frustrating you know, in Manchester you get a little bit here, but we got more play than we expected," batting coach Marcus Trescothick told the BBC.
"Today looked like a complete washout so it's a bonus. We're one wicket closer but it's still frustrating."
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Australia, who lead the series 2-1 and will retain the Ashes if the fourth test ends in a draw, resumed on 113-4, needing 162 runs to make England bat again.
Sensing opportunity at the outset, England began aggressively as they looked to take quick wickets and Mark Wood was tasked with leading the attack after his vicious spell on Friday decimated most of Australia's top order.
However, Wood and his fellow quicks failed to find a breakthrough.
Labuschagne and Marsh did well to soak up the early pressure, stealing singles and finding the occasional boundary to keep the scoreboard ticking as dark clouds continued to gather over the Old Trafford stadium.
Umpires then ruled that it was too murky to let England keep using their fast bowlers, forcing captain Ben Stokes to bring in spinner Moeen Ali and part-timer Root.
The change initially played into Australia's hands, with Labuschagne hitting Root for two sixes and two fours to bring up his first century in England, but a rare lapse in concentration led to the batter nicking a delivery through to Jonny Bairstow just before tea.
"Obviously it's always very special getting a test hundred. It doesn't happen too often but I'm disappointed I couldn't get us to tea," Labuschagne told the BBC.
"I feel like my game is in a really good space now. Coming into this game I was confident about my technique and how I was batting.
"I was able to be confident and go back to my strengths, forcing their hand to bowl a lot of balls at me and take time out of the game."
Labuschagne departed on 111, his highest test score outside Australia.
The rain returned soon after the players left the field for tea, and with the weather forecast for the rest of the day looking bleak, play was abandoned at 1730 GMT.
Britain's Met Office predicts showers throughout the day on Sunday as well.
