Russell Knox three off FedEx St Jude Classic lead in Memphis

Scotland's Russell Knox
Knox qualified for the 2013 US Open and finished in a tie for 45th place
FedEx St Jude Classic second round leaderboard
-9 B Koepka (US); -8 A Cook (US); -7 S Alker (NZ); -6 C Smith (US), R Knox (Sco), R Gomez (Arg), S Brown (US), T Gillis (US), G Owen (Eng), T Hoge (US) Selected others -3 B Davis (Eng), P Mickelson (US), L Donald (Eng); -1 M Laird (Sco); +5 P Harrington (Ire); +9 G McDowell (NI); +10 J Donaldson (Wal)

Scotsman Russell Knox returned a bogey-free 64 to move three shots off the lead at the halfway stage of the FedEx St Jude Classic in Memphis.

The 29-year-old world number 77 reached six under, matched by England's Greg Owen who carded a level par 70.

American Brooks Koepka, who won his maiden PGA title in February, posted a 67 to lead by one at nine under at the TPC Southwind course.

Padraig Harrington, Graeme McDowell and Jamie Donaldson all missed the cut.

Ireland's Harrington was four shots outside the cut line after adding a 70 to his opening 75, Northern Ireland star McDowell had seven bogeys in a 73 and finished nine over for the two rounds, while Wales' Donaldson had two triple bogeys in a 77 for a 10 over total.

Knox has now made the cut in 16 of his 20 PGA events this season and has eight finishes inside the top 25, with two third places including the Honda Classic in March.

Big-hitting Koepka made four birdies and a single bogey but said: "I still feel like I could be five or six under par more."

Fellow American Austin Cook, playing on a sponsor's exemption, is second after a 64 and he commented: "I feel like I should be out here. My irons were on fire and I holed some putts."

New Zealander Steven Alker reached 10 under but finished bogey, double bogey to drop to third place, a shot ahead of Knox who is tied for fourth.

Former world number one Luke Donald had three birdies in a 68 and is six strokes adrift at three under.

The Tennessee event is the final tournament on the PGA Tour before the US Open begins at Chambers Bay on Thursday.