The county youngsters thrived on a century opening stand between Middleton (77) and Tom Prest (56), with Basingstoke-groomed Metzger (70) inflicting further punishment on a tiring SW attack.
Only Tom Morton (33) made an impression as teenage spinner Mo Abbas (3-13) help send South Wilts crashing to 101 all out.
Alton’s two pre-season matches at Amersham and Farnham have produced a staggering 1,166 runs, with one defeat and one victory.
After the 587 run bonanza at Amersham, the Brewers immersed themselves in a 579-run fest at Farnham, where they ran out 19-run winners.
Michael Heffernan made a classy 84 for Alton, whose 299-6 was backed up by Scott Myers (44), Dan Harris (33), Mark Heffernan (27) and Joe Paul (25 not out).
Farnham made a decent fist of chasing down the target, but were eventually dismissed for 280, Jack Myers taking 4-69.
Liphook & Ripsley, in contrast, experienced an opening day to forget at Cranleigh, where they were skittled for 75 after the Surrey Championship side had posted 208-6, with former Kenya opener Seren Waters (son of Sparsholt legend David Waters) making 63.
Liphook lost eight wickets for 16 runs as they crashed from 41-2 to 57 all out.
Bournemouth, newly promoted to the Southern Premier Division this season, made a bright opening with a comfortable seven-wicket win over ECB Home Counties Premier Division outfit Horspath, who were dismissed for 158.
Luke Matthews, back from an Adelaide winter, scored an unbeaten 75 for the Lions.
Pagham sent two sides to Portsea island, where they beat Portsmouth (162, Joe Krooner-Evans 44)) by seven wickets, but were on the receiving end of a 255-6 towsing from Portsmouth & Southsea at St James’s Park.
Steve Clements (45) and Matt Benfield (41) got the show on the road for P & S, with Jack Davies hitting 50 and Jack Peach a brisk 31 not out. Keiron Dunstan (5-39) and Ben Saunders (3-33) combined to dismiss Pagham for 147.