Ferrer fired 53 winners in his 6-7 (6/8), 7-6 (7/3), 6-1, 6-1 win over Croatia's unseeded Ivan Dodig and goes on to tackle either Argentine eighth seed Juan Martin del Potro or Andreas Seppi, the 23rd seeded Italian.
The 31-year-old Ferrer, who was defeated in the French Open final by compatriot Rafael Nadal last month, will be playing in his seventh consecutive Grand Slam quarter-final.
Janowicz, the 24th seed, defeated 31-year-old Jurgen Melzer, who was hoping to become the first Austrian man to reach the last eight.
He was joined in the last eight just moments later when 31-year-old Kubot, the lowest-ranked player left at 130 in the world, defeated France's 111-ranked Adrian Mannarino, 4-6, 6-3, 3-6, 6-3, 6-4.
More From This Section
The last Pole to reach the last-eight at Wimbledon was Wojtek Fibak in 1980.
Later Monday, top seed Novak Djokovic, the 2011 champion, tackles 2009 semi-finalist Tommy Haas, the 35-year-old German 13th seed who is bidding to become the oldest Wimbledon quarter-finalist since Tom Okker in 1979.