In between, on 11 under par, lies Argentina's Angel Cabrera, who scored 67 yesterday, while local lad Gary Orr is among the chasers on nine under.
As the game's lesser lights again outshone the stars - despite dreamy, sun-drenched conditions that meant this picture-postcard course put up little defence - Clarke's round mirrored his mood, as the 37-year-old Ulsterman acknowledged.
"I don't know what's going on at the moment," he said, adding that his game "is more of a grind than playing really good golf". After a month's absence with wife, Heather, who has cancer, that is understandable.
"I haven't had time to work on my putting," Clarke added. A round containing a mere 22 putts, which Clarke's playing partner, Colin Montgomerie, said was "absolutely phenomenal", was testament to the input of Clarke's putting coach in recent days.
Clarke's calmness under pressure also played its part. He joked that even when he shanked his second shot on his opening hole yesterday - the 10th, he started on the back nine - he limited himself to "a little bit of a verbal seethe" rather than a full-blown, club-throwing wobbly.
Restraint paid dividends. He salvaged a bogey on the 10th after a terrible lie in the rough, the shank, and then a bunker shot.
Clarke's eagle, on the par-five 13th, came courtesy of a drive from the tee, a five-wood to the green and a 30-foot putt. The birdie on his 15th hole of the day - at the sixth, where the backdrop was mountains, loch and sunbathers aboard boats - was fashioned with a pitch from the rough to within five feet of the pin. The next birdie required a 15-foot putt, and the last two needed putts of four and six feet respectively.
Asked if he was confident that he could eliminate his inconsistencies, he summed up his situation with: "Confident, no. Hopeful, yes."
Dutchman Lafeber, up to No 139 in the world, has seen his stock rise in more ways than one. In 1997 he sold 7,500 shares in himself at around £30 each to businessmen, raising £250,000 to fund his long-term plans. Last year he repaid his investors, adding 85 per cent profit. The 30-year-old from Eindhoven hit a flaw-free round, holing four birdies on his way out, and four more on his way back. "When I woke up, it was beautiful weather, and no wind, a great day for scoring," he said. With the wide fairways here, and little or no breeze, it was almost target golf for those who took advantage.
Glaswegian Forsyth, and Orr, from nearby Helensburgh, both did. Five successive birdies around the turn underpinned Forsyth's 64, although he cautioned that two good days will not necessarily translate to four and a title. "It's just as likely I could shoot a 77 tomorrow," he said. "That's been my downfall - three rounds in the 60s and one 74 or 75. It's something I'm trying to put right."
The big names were mostly unexceptional, with Phil Mickelson carding 72 to finish three under par overall, Retief Goosen hitting 67 to go four under, and Ernie Els scoring 66 to lie six off the pace.
SCOTTISH OPEN (Loch Lomond) Leading early second-round scores (GB or Irl unless stated): 130 M Lafeber (Neth) 67 63; 131 A Cabrera (Arg) 64 67; 132 A Forsyth 68 64, Darren Clarke 67 65; 133 R Sterne (SA) 65 68; G Owen 67 66; 134 L Westwood 65 69; 135 T Jaidee (Thai) 66 69, T Lehman (US) 66 69, R Allenby (Aus) 68 67, S Dyson 71 64, N Dougherty 66 69, P Hedblom (Swe) 67 68, L Donald 68 67; 136 P Lawrie 65 71, P Golding 70 66, J Donaldson 71 65, D Carter 68 68, I Poulter 69 67; D Drysdale 67 69; E Els (SA) 70 66, M A Jimenez (Sp) 67 69; 137 T Price (Aus) 69 68, C Montgomerie 68 69, B Mason 72 65, E Romero (Arg) 70 67, D Lynn 69 68, A Scott (Aus) 70 67; Selected: 138 R Goosen (SA) 71 67, P Broadhurst 73 65, O Wilson 69 69, K Eriksson (Swe) 68 70, C Hanell (Swe) 69 69 F Jacobson (Swe) 71 67, D Griffiths 69 69, S Gallacher 68 70, S Wakefield 70 68, K Ferrie 67 71; 139 T Levet (Fr) 71 68, P Mickelson 67 72, S Drummond 72 67.