Only 25 overs were possible at the Ageas Bowl, though that was still long enough for Lancashire's Cypriot-South African batsman Andrea Agathangelou to complete his maiden century for his adopted county.
The 23-year-old made the most of his unexpected opportunity after replacing Simon Katich, who was hit on the head in the warm-up, moving from his overnight 93 to 121 before being run out by Danny Briggs.
Thanks to his efforts, Lancashire's last two wickets added 113. He and Glen Chapple put on 43 before another 70 came alongside last man Simon Kerrigan to frustrate Hampshire, who had been on top for most of the first day.
Lancashire resumed in gloomy, wet conditions at the start of the second day at 252-9 in the 82nd over and James Tomlinson and David Balcombe, who had taken seven of the wickets to fall, found the last pair in fighting spirit.
Agathangelou needed 20 balls to move to three figures and he dominated the last-wicket stand with Kerrigan offering solid, uncompromising support.
Together they put on a further 43 runs in 17 overs before Agathangelou was stranded by Briggs' throw. By then, though, Lancashire had fully recovered from a disappointing 182-8.
Balcombe overcame a horrific start in which he conceded 21 from his first three balls of the match to finish with 5-104 but Lancashire had held out for an extra 80 minutes in the process of regaining the initiative. Kerrigan was unbeaten with 14 at the fall of the last wicket.
Hampshire lost captain Jimmy Adams, leg before to an inswinger from Kyle Hogg, early in their reply. Michael Carberry and Liam Dawson took Hampshire through to 7-1 from eight overs at lunch, but then came the rain.
Umpires Nigel Cowley and Martin Saggers waited until 5pm before calling off play for the day but they were left with no alternative in the squally showers.