The former midfield maestro was expected to overhaul Madrid's game with a cerebral and tactically adroit approach, but his team flattered to deceive.
By the end, Madrid looked in similar shape to how they performed last season, where they ended up without a major trophy, as they were outplayed by rivals Barcelona in a 3-2 Spanish Super Cup final defeat on Sunday.
Four points behind the Catalan La Liga leaders and sitting seventh in the league phase of the Champions League, Florentino Perez took action and replaced Alonso with reserve team coach Alvaro Arbeloa.
The axe was above Alonso's neck, waiting to drop for several weeks, as a run of five victories kept him in his post until the Clasico in Saudi Arabia.
Alonso, who gained plaudits at Bayer Leverkusen after winning the Bundesliga undefeated in 2024, arrived at Real Madrid with dreams of leading the team to glory like Carlo Ancelotti or Zinedine Zidane before him.
However, his early dismissal leaves him among a less illustrious list of other swiftly ousted coaches, including Rafa Benitez and Julen Lopetegui.
Alonso would have liked a new midfield arrival in the summer after the departure of Luka Modric in the summer and Toni Kroos the year before, but none was forthcoming.
The team's performance at the Club World Cup in Alonso's first matches showed some early promise, despite the stinging 4-0 defeat meted out by Paris Saint-Germain in the semi-finals.
At Real Madrid, the squad's biggest names tend to rule the roost and despite a good start in terms of results, cracks began to show as Alonso's approach did not suit them.
The Basque manager rotated his pack heavily, to the chagrin of players like Vinicius Junior, who was benched on several occasions and hauled off early on others.
After being substituted in a 2-1 Clásico victory in La Liga in October, Vinicius showed his rage at Alonso. From that moment, things changed.
The coach did not make an example of Vinicius, and instead restored his near untouchable status - even through a run of 16 matches without scoring, which finally ended in Jeddah. Too little, too late.
Jude Bellingham also became an undisputed first choice after recovering from shoulder surgery, even though the England international's form has been inconsistent.
Youngsters who did well at the start of the season, including Arda Guler and Franco Mastantuono, found their game time limited.
Along with the return of the stars, some of Alonso's concepts faded out, too. High pressing vanished from the menu.
Madrid suffered a spate of injuries, which Alonso said was partly the reason for his team's change of approach, and it reduced his options.
Although the Clasico win over Barcelona bought Alonso some time, it seemed that president Perez was never convinced.
French superstar Kylian Mbappe was hammering the goals in but the team rarely flowed in attack, with too many cooks spoiling the proverbial broth.
Downward spiral
A 5-2 thrashing by Atletico Madrid in September was an early blot in Alonso's copybook, while even when Madrid were winning games, they were not overly convincing.
When Madrid hosted an NFL match at the Santiago Bernabeu in November, it meant more away matches grouped together in their schedule, contributing to a bad run of form.
They lost away at Liverpool in the Champions League, while Madrid were whistled by their own fans after a home La Liga defeat by Celta Vigo in December.
Spanish media reported that Alonso was given an ultimatum: defeat by Manchester City in the Champions League would spell the end for him.
City coach Pep Guardiola backed Alonso before the game, pointing out the difficulty of coaching one of Spain's giants.
"It's a difficult place, but he knows it, he has been here (as a player), he knows the reality," said the former Barca coach.
Despite a 2-1 loss, Alonso was given a stay of execution. The team's performance was improved, and players spoke out in support of the coach afterwards.
However, since then it felt like the first wrong move would end his reign.
Several wins were ticked off, although performances were largely still unconvincing, and Barcelona's Clasico victory offered the excuse Perez needed to act.
Alonso's replacement Arbeloa, promoted from the reserve team and also a former Madrid player, is another who knows the club inside out and the volatility of the hotseat that awaits him.