His nine under par, which equalled Ian Woosnam's course record, following his previous day's opening 66, gave him a five-stroke half-way lead over Paul McGinley and Woosnam - the latter pursuing his third successive victory in the event.
The only other players to have scored 60 in Europe are Baldovino Dassu, of Italy, in the 1971 Swiss Open, David Llewellyn, of Wales, in the 1986 Biarritz Open and Woosnam in the first of his Monte Carlo wins two years ago.
Clarke's card looked even more impressive at one stage, with a total of 59. His playing partner, Ken Brown, had marked him down for an extra birdie on the sixth hole. 'I wish it was,' Clarke said. 'But I only parred it. I've had a 61 at my home club Dungannon, while my previous best on tour was 66.'
That came in the same event here last year when he went to the turn in 28, only to cover the inward half in 38. This time he started on the 10th, got five birdies in six holes from the 13th to turn in 30 and 'just kept going and going'.
He putted from eight feet on the second, 10 feet two holes later and then pitched to a yard at the seventh.
At the ninth, a 59 - and with it the record and a pounds 14,000 prize - was on the cards if Clarke could hole his seven-iron approach. However, it ran 10 feet past the flag, but the putt presented no problem. His 36-hole total of 126, 12 under par, was one outside the European record.
Before yesterday Clarke's best finish as a professional was his fourth place in Morocco in April. He finished 112th on tour last year and currently stands 75th in this season's table.
McGinley followed up his first day 65 with a 66. 'I don't think there's pressure on me because nobody expects me to win,' he said.
Woosnam added a 65 to his opening 66, only to find himself slipping from two behind to five adrift. He remains favourite, however, for a pounds 75,000 first prize that would make him the first player to win the same title three years in a row since Peter Thomson won the Open in 1954-56.
MONTE CARLO OPEN (Mont Agel) Leading second-round scores (GB and Irl unless stated): 126 D Clarke 66 60. 131 P McGinley 65 66; I Woosnam 66 65. 133 R Gonzalez (Arg) 71 62; P U Johannsen (Swe) 68 65; P Mitchell 68 65; P Senior (Aus) 67 66; E Romero (Arg) 67 66. 134 R Davis (Aus) 68 66; M McNulty (Zim) 67 67; P Walton 68 66; D Mijovic (Can) 69 65; J Rystrom (Swe) 70 64. 135 J Sewell 67 68; D Edlund (Swe) 72 63; C Rocca (It) 64 71; M A Jimenez (Sp) 67 68. 136 K Waters 66 70; E O'Connell 70 66; P McWhinney (Aus) 70 66; R Boxall 74 62. 137 T Johnstone (Zim) 71 66; W Grant 66 71; J Hobday 69 68; G Levenson (SA) 69 68; M Mackenzie 71 66; M Gates 74 63; M Miller 70 67. Selected: 139 S Ballesteros (Sp) 70 69.Reuse content