La Union are rock bottom of the La Liga table, picking up just 10 points from their 28 matches this season, and the team are still waiting for their first league victory of the campaign.
UDA led Sevilla on Monday evening before trailing 2-1 late on, but they managed to claim a share of the spoils courtesy of an effort from Marezi in the fifth minute of added time at the end of the 90.
The result left Almeria 14 points from safety and saw them create an unwanted record, becoming the first team in the history of La Liga to go 28 successive matches without a win.
Garitano was appointed head coach last October, but he has now departed with a record of one win, seven draws and 13 defeats from 21 matches, with the victory coming in the Copa del Rey against Talavera.
"It's not normal to not have won yet, it seems incredible," Garitano said on Monday evening in his press conference following the clash with Sevilla.
"Although the opponents we had were very strong, we played a great game. It's a shame, we've been close to achieving it once again.
"We're going into the competition with our heads held high, competing fiercely in every single game and always close to winning. We'll try to get that first victory, the team is alive."
However, Almeria announced on Wednesday afternoon that Garitano had departed as manager.
"UD Almeria and Gaizka Garitano reach an agreement that ends the relationship between both parties. The club thanks the coach for his professionalism during his time as a Rojiblanco and wishes him luck in the future," read a statement.
Almeria then announced that Mel had become the club's new head coach for the rest of the season.
"Pepe Mel has been appointed as the new UD Almeria head coach after former gaffer Gaizka Garitano has parted ways with UD Almería," read a club statement on their official website.
"This replacement has taken place this Wednesday afternoon once the Bilbao-born coach has signed his departure and the new head coach has put pen to paper on his deal until the end of the present 2023/24 season."
Mel, who will be in charge for Sunday's La Liga clash with Las Palmas, left Greek outfit OFI Crete last month.
The 61-year-old last managed in Spain during the 2022-23 campaign, taking charge of Malaga, while he has also been in control of the likes of Getafe, Alaves, Rayo Vallecano, Real Betis, West Bromwich Albion, Deportivo La Coruna and Las Palmas during a well-travelled career.