"I reached a point where I felt that the whole staff were fractionalized, that the best thing to do to get this thing back was to make a change," Davis said during a lengthy news conference. "It hurts because I picked the guy. I picked the wrong guy."
The Raiders promoted offensive line coach Tom Cable to interim head coach.
Kiffin had a 5-15 record since being hired last year, losing his final game, 28-18, on Sunday to the San Diego Chargers.
The decision to remove Kiffin was more about his frequent criticisms of Davis' franchise than the team's performance on the field. Those critiques reached a peak when Kiffin distanced himself from the defense after a blowout loss in the season opener, saying that was under coordinator Rob Ryan and Davis' control.
However, during the news conference, Davis also critiqued several of Kiffin's coaching and personnel decisions. Among other things, he said Kiffin objected to the Raiders using the first pick in the 2007 draft on quarterback JaMarcus Russell.
"I didn't think it was any one thing. It was a cumulative thing," Davis said.
The Raiders said Kiffin was fired for cause, meaning they will likely try not to pay him for the remainder of his contract. He signed a three-year deal worth about $6 million when he took over last year.
Kiffin's agent Gary Uberstine had no comment and said he advised his client not to hold a news conference today. Kiffin instead will make his case directly to the commissioner in a grievance.
Kiffin told ESPN he was "embarrassed" for Davis while watching the news conference.
"It was very painful for myself and my family," he said. "A lot of accusations being made there, a lot of information being put up there, a number of lies."
Davis, 79, was front and center for more than 90 minutes, sharing the stage with Cable for some of that time.
Dressed in Raiders silver and black, Davis sat at a podium reading from notes illuminated by a large desk lamp. He seemed angry at times, blaming Kiffin for most of the Raiders' woes, though he also blamed himself for hiring him in the first place.
The firing comes a day after the St. Louis Rams let go of Scott Linehan, marking the second firing at the quarter point of the season. The last time a coach had been fired this early in the season was when Davis got rid of Mike Shanahan after four games in 1989.
Kiffin's job security was in question as far back as January, when a dispute with Davis over whether he could replace Ryan as defensive coordinator led to a resignation letter being drafted for the coach. Kiffin refused to sign it.
Oakland has an NFL-worst 20-64 record since the start of the 2003 season.
Kiffin, the son of longtime NFL defensive coordinator Monte Kiffin, was just a 31-year-old assistant at Southern California when Davis hired him to replace Art Shell in 2007. With that, he became the youngest head coach in the NFL's modern era.
Rams:: Quarterback Marc Bulger got his job back, the biggest development of new coach Jim Haslett's first full day in charge of the winless team. Backup Trent Green started Sunday's 31-14 loss to the Bills in Linehan's final game as coach. Haslett said Bulger will be the starter the rest of the season. St. Louis has a bye week before playing at Washington on Oct. 12.
Dolphins:: Ricky Williams said he was briefly tempted to smoke marijuana during Miami's bye weekend, an act that could have ended his roller-coaster NFL career. Williams has been in the league's substance-abuse program since 2002 and has tested positive for marijuana. Williams told The Miami Herald for yesterday's editions that when players were given Friday off, "automatically your mind, which is so constrained since training camp began ... says, 'I'm free, what can I do?' ... But I just thought about what I have to lose, and it was easy." Since 2004, the running back has played only 16 NFL games, including three this year. If Williams were to smoke marijuana again, he would likely be out of the NFL for good because he has violated the league drug policy four times.
Steelers:: With Willie Parker and Rashard Mendenhall injured and out, division-leading Pittsburgh is down to one healthy running back for Sunday night's key AFC game in Jacksonville - Mewelde Moore. Parker will miss his second straight game with a strained knee. Mendenhall, a rookie, needs surgery for a fractured right shoulder and will miss the rest of the season. He was hurt while being hit by Ravens linebacker Ray Lewis during the Steelers' 23-20, overtime win Monday night. In addition, fullback Carey Davis has a sprained ankle and might not play Sunday night and right guard Kendall Simmons ruptured an Achilles tendon and won't play again this season.
Bengals:: Running back Cedric Benson signed with the team, which was undeterred by two alcohol-related arrests that prompted the Bears to let him go. Benson will take the spot of running back DeDe Dorsey (hamstring), who was put on injured reserve. Chris Perry is Cincinnati's starting running back.
Et cetera:: Tony Mandarich, the offensive lineman who was the No. 2 pick in the 1989 NFL draft by the Packers and was a bust in the league, said he used steroids at Michigan State and faked a drug test before the 1988 Rose Bowl. He also said during an interview on Inside the NFL that will air today on Showtime that he did not use steroids in the NFL but was addicted to alcohol and painkillers. ... A preliminary hearing on a drunken-driving charge for Titans defensive end Jevon Kearse has been continued until Jan. 6. ... Giants backup running back Danny Ware was arrested and charged with an alcohol offense while walking in the road early Sunday in Athens, Ga., and released on $500 bond.