Surrey 42 for 4 (Barker 3-15) trail Hampshire 488 (de Grandhomme 174*, Organ 67) by 446 runs
A magnificent 174 not out from Colin de Grandhomme put Hampshire in full control of the LV= Insurance County Championship Group Two clash against Surrey at the Ageas Bowl.
The New Zealand Test all-rounder became only the eighth Hampshire player to score a debut first-class century as Surrey's under-manned attack, still missing injured Kiwi quick Kyle Jamieson, were put to the sword by an inspired lower order who added 259 for the last three wickets to score 488 having started the day on 229 for 7.
Surrey were 42 for 4 at the close following a fine spell of bowling from Keith Barker who posted figures of 3 for 15 from 10 overs.
Former South Africa batter Hashim Amla - a double centurion when the sides last met in May at the Kia Oval - was unbeaten on 24 and Will Jacks 1 not out before rain and bad light stopped play with Surrey needing another 296 runs just to avoid the follow-on.
De Grandhomme, who came to the crease on day one when his side were struggling at 135 for 4, was in imperious touch with the bat, hitting 17 fours and three sixes on his way to his highest first-class score in a memorable first red-ball appearance.
The 34-year-old was well supported by Felix Organ's enterprising 67 and No. 11 batter Brad Wheal who chipped in with a career-high 45 as Hampshire posted an imposing total in their push for a victory that would greatly enhance their prospects of a top-two finish.
Having spent a day-and-a-half in the field, Surrey then got off to the worst possible start when Mark Stoneman departed for a golden duck from the opening ball of Kyle Abbott's first over.
Abbott sent down a peach of a delivery that the former England opener had no option but to play at and Joe Weatherley took a sharp diving catch.
That early loss was compounded by the exit of Surrey captain Rory Burns just before tea.
Barker found the edge of the England man's bat and Weatherley took another sharp grab at second slip as the visitors fell to 8 for 2.
Left-arm seamer Barker then struck twice more after the restart in a superb maiden over, rattling the stumps of Ryan Patel and Jamie Smith before the players were taken off by umpires Ian Gould and Chris Watts.