The all-rounder top scored with 101 to help Sri Lanka to 302-6 on their way to an 87-run battering of Alastair Cook's men in Colombo on Tuesday, as the hosts completed a 5-2 series victory.
Dilshan - who was playing his 300th ODI - then took 3-37 from 10 overs with the ball as England were bowled out for 215 in reply.
With the World Cup two months away, the 38-year-old believes the team are hitting top form at just the right time.
"It was a great way to finish this year with the hundred," he said.
"I've been happy with the all-round performance this series. Just before the World Cup, it's the right time to peak."
Sri Lanka captain Angelo Mathews also paid tribute to Dilshan's knock, but is keen for the team to quickly turn their attentions to the two-Test series in New Zealand, which starts on December 26.
"It was a great team effort I thought," he added. "Dilshan was tremendous with runs and wickets.
"We're really excited ahead of the World Cup, but first thing's first, we'll enjoy this series win tonight and then get on the plane to New Zealand tomorrow and start our preparations."