Sussex opener Tom Clark scored a century in a rain-shortened pre-season friendly.
Sussex resumed on the second day at 60/1 after bad light halted proceedings on the first day.
Clark and Alsop (32) put on 124 runs for the second wicket partnership, with Clark hitting the boundary twenty times on his way to reaching three figures.
Cam Steel made the breakthrough when Alsop clipped the ball to Jamie Smith at short leg. Clark reached his century shortly after and duly retired.
Sussex reached a score of 165/3 at lunch. Unfortunately, the game was suspended for the day due to rain.
Surrey will face Kent in a pre-season friendly at The Kia Oval on Thursday and Friday. The gate will be open for both days.