Walsh has thrown 21.50m to claim his penultimate event of the European season, shading Aussie Damien Birkenhead by 15cm.
Commonwealth champion O'Dayne Richards of Jamaica finished fourth (21.00m), while American Joe Kovcacs, the man dethroned by Walsh in London earlier this month, could only muster 20.85m for fifth.
Walsh's archrival, American Ryan Crouser, did not compete.
His next event is the IAAF world challenge is on Friday.