Hampshire 292 for 3 (Alsop 127*, Holland 114) vs Gloucestershire
Hampshire closed the day on 292 for 3 to continue their excellent start to the season, with Alsop unbeaten on 127 at the close with nightwatchman Mason Crane yet to score.
Sam Northeast was dismissed for 24 in the penultimate over of the evening when he was caught down the leg-side by James Bracey off Matt Taylor.
Both sides went into the game on the back of victories in their opening two matches.
However, the visitors were rocked before the match by news they could not field all-rounder Graeme van Buuren due to delays in his paperwork after complications around Brexit changed his eligibility status to that of an overseas player.
South African Van Buuren scored a match-winning century in the win over Surrey two weeks ago and is also the side's front-line spinner. But he had to be left out of the team after the club received the news with West Indies batsman Kraigg Braithwaite and Australia quick Dan Worrall already named in the team.
Holland followed up on the unbeaten 146 he chalked up against Middlesex last week with a patient knock of 114 on a good batting pitch that offered little for the bowlers.
The visitors, who also took the impressive scalp of Somerset last week, made an early breakthrough when Dominic Goodman struck with his first delivery of the match.
The 20-year-old seamer, who is still a student at Exeter University, took three wickets on his debut at Taunton last week and he trapped Joe Weatherley lbw for just eight, leaving the opener as the only player in the Hampshire top-six not to pass at least 100 this season.
With little in the slow-paced surface to offer encouragement to the bowlers, Worrall did manage to find the edge of Holland's bat when he was on 77, only for Braithwaite to put down the most straight-forward of slip catches.
After resuming after tea on 90, Holland chalked up his third career century with a flick through square leg off Josh Shaw.
Alsop's second century of the campaign was punctuated with two glorious straight drives down the ground and a series of venomous cut shots to the boundary as he brought up three figures for the fourth time in his career.
Worrall finally got the breakthrough he deserved when he ended the 228-run stand for the second wicket when he trapped Holland on the back of his crease, leaving umpire Ben Debenham with a simple lbw decision.