He was replaced by Alonzo Powell, a former Mariners outfielder and, for the past three seasons, the hitting coach for Triple-A Tacoma.
"It is a difficult day when you like someone and are very fond of a person like Alan, who has worked his tail off," general manager Jack Zduriencik said. "But you get to a point where you have to make a judgment call, and that decision was made today."
The move comes days after several personnel moves, including the release of outfielder Eric Byrnes, were made in an attempt to shake up a stagnant offense, which ranks last in the American League in most categories.
The Mariners, who went into Sunday's series and homestand finale on an eight-game losing streak, are last in batting average (.225), runs scored (94), hits (222), RBIs (89) home runs (10), slugging percentage (.315) and on-base percentage (.302).
"I have a lot of respect for Alan," Mariners manager Don Wakamatsu said. "From the day he got here, he's been nothing but professional and has worked as hard as anybody on this staff.
"Unfortunately, when things don't go the way you want it, a change needs to be made. There are eight guys hitting under .220. That can't continue and you have to start somewhere. Alan is the guy that has to pay the toll for that."
Of the regular-position players, center fielder Franklin Gutierrez is the only Mariner that has a higher batting average this year (.322) than his career average coming into the season of .268.
Cockrell, who was in his second season with the Mariners, reported to work early Sunday morning and was in the video room behind the first-base clubhouse watching film of Angels starter Ervin Santana, "when Wak came and got me."
Several minutes later, Cockrell was informed of the move, exchanged hugs with the early-arriving players and departed.
"When you don't hit, you have to make a move and they made a move." Cockrell said. "I don't want to say anything that I am going to regret later on. We struggled in the area of driving in runs. You know, that was the biggest issue. We preached quality at-bats, we preached wearing on a pitcher, but in all honesty, it would take three or four quality at-bats consecutively to score one run.
"That puts a lot of pressure on the offense and it's tough to do at this level inning after inning. For me, that's where we came up short. I tried to do what I could do every day. It didn't work out. It just didn't work out."
Cockrell returned to his Colorado Springs home on Sunday afternoon.
Veteran designated hitter Mike Sweeney, batting .176, went to bat for Cockrell and said the hitters are responsible for the lack of offense.
"I look around this clubhouse and there are a ton of players that deserve to get fired before him, and I am one of them," Sweeney said. "I mean, I know our offense hasn't had a heartbeat, but it's not due to Alan Cockrell. It's due to us, the players.
"We are the ones that deserve all the criticism, not him. I will be the first one to stand up and take a bullet for that guy because he was here early, he worked his butt off, he put in more hours than anyone in this clubhouse. It's tough to see a guy like that go. I wish I was the one to go instead of him because I deserve it more than he does. It's brutal.
"I know Jack has a tough job as the GM and when the offense isn't going, the first person you point a finger at is the hitting coach. If the fans could see the work 'Ace' put in the cage, video room, counseling guys after games, he was the epitome of a pro and one of best hitting coaches I've ever had. So it's a tough day for us."
Several players agreed with Sweeney and shouldered most of the blame for the coaching change.
"I am kind of sad," Gutierrez said. "I know this is baseball and it's a business. It's bad, but somebody has to pay. I don't think it was his fault. Nobody is saying that. Everybody is going through a tough time right now.
"I think he is a great guy, a great friend and a great hitting coach, but this kind of thing happens and there's not a lot you can do."
Zduriencik said he understood the players' feelings and didn't disagree.
"To me, it's interesting. You look at our ballclub and see so many players playing under their career norms," he said. "I think if we can just get back to having our players be what they are offensively, then we're certainly a much better ballclub.
"The fact so many guys have not played to that level, there's a responsibility. And I can understand where a player would look internally and say, 'Look where my batting average is and I'm responsible for that.'"
The Mariners were expected to prosper with small-ball this season, especially with switch-hitting Chone Figgins being signed as a free agent and placed in the lineup behind Ichiro Suzuki.
Figgins went into Sunday's game with a .192 batting average, which has been offset somewhat with a team-leading 23 walks.
The position players are batting an accumulative 400 points lower than their career batting averages.
"I know Jack is doing his job and he has to send a message," Sweeney added. "I'm sure the same message could be sent by releasing some players, or sending them down, and that could be more justified.
"We are the ones stinking up the place. We have to just go out there and do it. We have the manpower to be better than we are."
Jim Street is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.