The County fell short in a mammoth run chase at York Cricket Club, having allowed an inexperienced Vikings side to smash a huge 353 for nine in a match reduced to 46 overs per side by rain.
But it wasn’t enough as a Yorkshire side missing nine players on duty at The Hundred, eased to a Group B victory, bowling Northants out for 320 with 10 balls remaining.
It was a disappointing result and performance from a Steelbacks team that was close to full strength, although Ben Sanderson, Simon Kerrigan and Luke Procter were rested, and Brandon Glover missed out through injury.
Yorkshire were dominant with the bat, with Will Fraine (143) and Harry Duke (111) putting in 209 for the first wicket, before teenager Will Luxton smashed 83.
And McManus admitted his and his team-mates’ performance simply wasn’t up to scratch.
“Ultimately it’s a loss, which isn’t the way we wanted to start the competition,” said McManus, who has been on loan all season, but was playing his first match after signing a permanent deal with Northants on Monday.
“But, if we’re honest, we weren’t at our best today and we’ve still got within touching distance. That’s a positive.”
Northants were always just about in the chase until the closing stages, with their hopes disappearing once McManus was dismissed.
“We wanted to take the chase as deep as possible,” said the wicket-keeper, who won the One Day Cup with Hampshire in 2019.
“Wickets in hand at the back end of a 50-over chase is crucial.
“We knew that with the wind and a short boundary, we’d be in with a chance.
“We’re on the right track, but we didn’t quite execute.”
Northants must now shrug off this defeat and get themselves ready for their next encounter when they host Essex at the County Ground on Sunday (11am).
And McManus is promising the Steelbacks fans that will be the case.
“We’ve got a quick turnaround with another game in a few days’ time,” said the former Hampshire man.
“So hopefully there are a few sharpeners for us all and we can get back to winning ways.”
Essex’s opening clash at Lancashire on Tuesday was rained off without a ball being bowled, but they are due to get the campaign up and running on Friday when they host Derbyshire.