Former England batsman Hick added the seven runs he needed overnight to reach three figures and become only the eighth man to score a century of centuries for one county.
It was also the 40-year-old's 130th first-class hundred ton and he is now the sole occupant of eighth place in the all-time list of century-makers.
He was eventually dismissed for 139 by England spinner Monty Panesar but Worcestershire, after running up 600s in their last two Championship matches, were well set for victory after declaring at 543 for nine.
And their position was strengthened by India paceman Zaheer's haul of five for 27 as Northamptonshire were shot out for a paltry 76. Following-on, the visitors were 76 for two at stumps.
Elsewhere, Michael Vaughan's comeback from injury was interrupted by a hamstring problem, meaning he was unable to field for Yorkshire at Arundel.
The England captain did not return after lunch as Yorkshire were left on the backfoot against First Division title contenders Sussex.
With Vaughan off the field, Murray Goodwin hit a double century as Sussex built a huge lead.
Former Zimbabwe batsman Goodwin hit 235 with captain Chris Adams adding 107 to take Sussex to 479 for seven, an advantage of 241 runs.
At the Rose Bowl, Durham inflicted a crushing defeat on Sussex's southern neighbours Hampshire, winning by 227 runs after Australian Callum Thorp finished with match figures of 11 for 97.
Meanwhile First Division leaders Lancashire, chasing their first outright championship title since 1934, put themelves in position for another conclusive victory, against Middlesex at Lord's.
Luke Sutton (72) and Kyle Hogg (70) took their sixth-wicket partnership to 117, building on Australian Brad Hodge's 161, as the visitors amassed 505 despite Middlesex and New Zealand all-rounder Scott Styris's six for 71.
Former England international Dominic Cork took four wickets as Middlesex were bowled out for 161 and made to follow-on. They were 47 for one at stumps.
In other matches Australian Andy Bichel took six for 38 on his debut for Essex to help his new side overcome Derbyshire by eight wickets in the Second Division clash at Derby.
Derbyshire could muster just 162 in their second innings, leaving Essex just 89 to win, a task completed in 19 overs, with a day to spare.
Mark Ramprakash's run-spree for Surrey continued as the ex-England batsman struck another century this season as the visitors fought back well against Glamorgan at Swansea.
The Welsh county had been 62 runs ahead on first innings after being bowled out for 410 but Ramprakash ensured they would face a stiff chase on the final day.
Ramprakash was 110 not out at stumps, having put on 125 with Jon Batty, with Surrey 261 for three.