Alviro Petersen overshadowed Graeme Smith's debut as Surrey captain with 167 to put Somerset in a strong position in their County Championship match at the Oval.
As his South African opening partner, Petersen's qualities are well known to Smith and they were evident for much of a day which ended with Somerset on 344-8.
Petersen came in to make his debut innings for his third county in the seventh over after England opener Nick Compton had played on to Jade Dernbach for a duck and, while his team-mates often struggled to time their shots on a slow pitch, he did not offer a chance on the way to the 31st first-class hundred of his career.
Strong on the leg side against both seam and spin, Petersen looked on course to repeat the double hundred he made at the Oval for Glamorgan two years ago when Zander de Bruyn trapped him leg before as he tried to work the ball through midwicket. He batted for 312 minutes, faced 255 balls and hit 19 fours and a straight six off Batty.
Petersen was the only batsman to look totally at ease in the conditions as the rest of Somerset's top-order struggled to match his fluency.
Skipper Marcus Trescothick (25) looked in good touch until he misjudged Gareth Batty's arm ball in the off-spinner's second over. Petersen then added 59 for the third wicket with James Hildreth (34) before Hildreth played on to Dernbach - the pick of the Surrey attack - in the first over after lunch.
It was Surrey's only success of the afternoon session as Petersen and Craig Kieswetter - two of the eight South African-born players taking part - added 143 in 42 overs for the fourth wicket with few alarms.
Kieswetter had moved to 43 without too many problems until he had a reckless charge down the wicket at Batty and was easily stumped and when Dernbach took the second new ball he dragged Surrey back into contention with two wickets with successive deliveries.
Jos Buttler left a ball that nipped back to hit his off stump then Peter Trego edged the next delivery to another Surrey debutant, Vikram Solanki, at second slip.
Alfonso Thomas survived the hat-trick and was still there at stumps by which time the otherwise wayward Stuart Meaker had picked up his first wicket when he bowled Jamie Overton.