Lewis was on 129 after an unbroken eighth-wicket stand of 88 with James Boiling that hauled the hosts up from 127 to 215 for 7 by the close. Their captain, David Boon, was out for a duck.
Mark Ramprakash led his Middlesex side out of trouble at Bristol against erstwhile leaders Gloucestershire, for whom Mike Smith took 5 for 23 in 18 overs.
Middlesex were 47 for 5 before their new captain made 75 to help them reach 237. Before the close Angus Fraser took two of three Gloucestershire wickets to fall with only 57 on the board.
Matthew Hayden, the Australian left-hander, scored his fourth century in as many matches for Hampshire, put in to bat by the bottom side Northamptonshire at North- ampton.
Hayden struck 27 boundaries in his 150 and put on 189 with Kevan James (56) and 79 with Robin Smith (71no) as the visitors reached 335 for 4 by the close.
Jason Ratcliffe and Alistair Brown both scored centuries as Surrey's batsmen tucked into the Worcestershire bowlers at New Road to score maximum batting points.
The former Warwickshire batsman Ratcliffe, 28 on Friday, raced to three figures off 160 balls with 17 fours and a six off the first delivery of the day from Bobby Chapman. He put on 179 in 38 overs with Brown, whose 121 was his second century in four innings. Surrey finished the day on 382 for 7.
Iain Sutcliffe hit his maiden Championship century as Leicestershire dominated the opening day against Somerset at the Bath festival.
The 22-year-old former Oxford University batsman scored 112 in a total of 337 for 3 off 100 overs against an injury-hit attack after the visitors had won the toss.
It was a bad day for Somerset, who lost newly capped pace bowler Andre van Troost with a hamstring injury and their Pakistani leg-spinner, Mushtaq Ahmed, with a knee problem.
Glamorgan's Steve James was left one run short of his century when rain prevented any further play against Lancashire at Liverpool.
James had made a brilliant 99 not out, with Adrian Dale unbeaten on 34, as Glamorgan moved to 173 for 1, James' opening partner Hugh Morris the man out.Reuse content