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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.
Ferrer insists that the ankle injury which he has carried into Wimbledon will not be a problem.
"There is a little bit of pain, but it's normal. It's impossible to play without any pain," he said.
Janowicz, the 24th seed, defeated 31-year-old Jurgen Melzer, who was hoping to become the first Austrian man to reach the last eight.
The 22-year-old Janowicz's 3-6, 7-6 (7/1), 6-4, 4-6, 6-4 win was based on 16 aces and 34 winners as he reached his first Grand Slam quarter-final.
He was joined in the last eight just moments later by 31-year-old Kubot, the lowest-ranked player left at 130 in the world, who defeated France's 111th-ranked Adrian Mannarino, 4-6, 6-3, 3-6, 6-3, 6-4.
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.
Djokovic has a 5-3 career record over the world number one, but Haas defeated him at the quarter-final stage on his way to the 2009 last-four.
Victory on Monday would give Djokovic, who has yet to drop his serve in three rounds so far, a 17th successive place in a Grand Slam quarter-final.
Haas is playing in his 53rd Grand Slam, just four behind the record of 57 for active players held by Roger Federer and Lleyton Hewitt.
Second seed Andy Murray, the runner-up to Federer last year, faces Russian 20th seed Mikhail Youzhny and is bidding to make the quarter-finals for a sixth successive season.
The shock defeats suffered by Federer and Nadal in the first week have helped throw the tournament wide open with only five of the men's top 10 seeds -- Djokovic, Murray, Ferrer, Tomas Berdych and Del Potro -- reaching the fourth round.
Five players -- Seppi, Janowicz, French world number 80 Kenny de Schepper, Mannarino and Dodig -- were all making their Wimbledon last-16 debuts.
Berdych, the seventh seed and 2010 runner-up, takes on unseeded Australian Bernard Tomic, a quarter-finalist in 2011.
Del Potro, the 2009 US Open winner, will be looking to make the quarter-finals for the first time when he meets Seppi who hopes to reach the last-eight of any Grand Slam at the 34th attempt.
The last Italian man to reach the Wimbledon quarter-finals was Davide Sanguinetti in 1998.
Spanish former top-10 player Fernando Verdasco faces De Schepper, who is playing in only his fifth major at the age of 26.
Results from the seventh day of Wimbledon (x denotes seeded player):Men's singles:
Fourth round:
Novak Djokovic (SRB x1) bt Tommy Haas (GER x13) 6-1, 6-4, 7-6 (7/4)
Tomas Berdych (CZE x7) bt Bernard Tomic (AUS) 7-6 (7/4), 6-7 (5/7), 6-4, 6-4
David Ferrer (ESP x4) bt Ivan Dodig (CRO) 6-7 (3/7), 7-6 (8/6), 6-1, 6-1
Juan Martn Del Potro (ARG x8) bt Andreas Seppi (ITA x23) 6-4, 7-6 (7/2), 6-3
Lukasz Kubot (POL) bt Adrian Mannarino (FRA) 4-6, 6-3, 3-6, 6-3, 6-4
Jerzy Janowicz (POL x24) bt Jurgen Melzer (AUT) 3-6, 7-6 (7/1), 6-4, 4-6, 6-4
Fernando Verdasco (ESP) bt Kenny De Schepper (FRA) 6-4, 6-4, 6-4
Andy Murray (GBR x2) bt Mikhail Youzhny (RUS x20) 6-4, 7-6 (7/5), 6-1
Women's singles:
Fourth round:
Sabine Lisicki (GER x23) bt Serena Williams (USA x1) 6-2, 1-6, 6-4
Kaia Kanepi (EST) bt Laura Robson (GBR) 7-6 (8/6), 7-5
Agnieszka Radwanska (POL x4) bt Tsvetana Pironkova (BUL) 4-6, 6-3, 6-3
Li Na (CHN x6) bt Roberta Vinci (ITA x11) 6-2, 6-0
Sloane Stephens (USA x17) bt Monica Puig (PUR) 4-6, 7-5, 6-1
Marion Bartoli (FRA x15) bt Karin Knapp (ITA) 6-2, 6-3
Petra Kvitova (CZE x8) bt Carla Surez (ESP x19) 7-6 (7/5), 6-3
Kirsten Flipkens (BEL x20) bt Flavia Pennetta (ITA) 7-6 (7/2), 6-3
