Signal faults, train and track impairments have been blamed for late V/Line services in May.
Punctuality on the Warrnambool line dropped over four per cent on last month's promising figures, with just 87.2 per cent of services arriving at their destination on time according to data released by Public Transport Victoria.
It's a step up from the same time last year, when punctuality was only 72.9 per cent.
In April Warrnambool train passengers enjoyed the line's best on-time performance in 12 months, with results 10 per cent better on the month before and the best since April 2018.
Less trains were on-time in May than April, even though buses replaced trains for two weeks in April.
Reliability on the Warrnambool line was 97.8 per cent in May, above the monthly target of 96 per cent.
A V/Line spokeswoman said it was the second-best result for 2019 and highest May result since 2016, when 85 per cent of trains were on time.
"Last month across the network, we recorded our second-best result for on-time performance this year and the highest May result since 2016," a V/Line spokeswoman said.
"In May the Warrnambool line exceeded the reliability target with its highest result since October 2018.
"Several train, track and signal faults impacted punctuality on the Warrnambool line last month."
Of a total 232 scheduled services either way from Warrnambool to Melbourne, 227 departed from their origin as planned.
Have you signed up to The Standard's daily newsletter and breaking news emails? You can register below and make sure you are up to date with everything that's happening in the south-west.