The Mercedes driver overhauled a 22-second deficit to title rival Max Verstappen after an aggressive call was made to make a second pit-stop to take his third victory of the season.
With stories emerging all the way through the field, let's dive straight into five lessons we learned at the Circuit de Barcelona-Catalunya.
Mercedes is the new favourite
Red Bull looked the team to beat in Bahrain after dominating testing and the first four sessions of the race weekend but after Hamilton stole the win, there has been debate between Toto Wolff and Christian Horner as to who was the title favourite.
In Spain, at a circuit known for its all-round characteristics that give a true impression of how a car will perform, Mercedes were a step ahead of Red Bull, particularly in the race.
Despite Verstappen getting the jump on Hamilton into turn one, it always looked like the reigning champion had the edge over the Dutchman given how close he was able to shadow the Red Bull driver.
And just when it looked like Hamilton was finally close enough out of the final corner to make a move into turn one with DRS, he dived into the pits for the crucial second stop that would ultimately hand him victory.
With a pit-stop gone wrong for Red Bull combined with Mercedes forward-thinking to save a set of medium tyres during practice, it was not just on track the champions prevailed, but their brains worked faster as well.
Ricciardo shows signs of his best
It would be fair to suggest there was a degree of concern about Daniel Ricciardo's start to life at McLaren, not least from the Australian himself.
Of course, the bedding-in period at Woking was always going to take a few races but a Q1 elimination in Portimão was an eyebrow-raiser that led team principal Andreas Seidl to set a deadline for excuses to stop.
Due to Ricciardo's race, it will feel like points gained from Ferrari for McLaren rather than points lost.
Alpine emerging as fifth best
Where has this speed come from for Alpine? Fifth in qualifying for Esteban Ocon was a superb effort whilst Fernando Alonso continued his acclimatisation with a top 10 grid spot.
The strategy in the race, however, did not quite play the way of the team, with Ocon slipping to ninth, while a second stop for Alonso demoted him to 17th despite battling for the final point for much of the event.
The raw speed difference between the Alpine of the first two races and the most recent two have confirmed the team as a solid points scorer.
Now, if it can get to grips with the medium tyres on race day, fifth in the constructors' championship will come at ease.
AlphaTauri architects of own downfall
In the first three races of the season, AlphaTauri's pace was obvious, only to shoot itself in the foot. Spain, unfortunately, was no different.
The number of points dropped by AlphaTauri may have already taken away any possibility of challenging Ferrari and McLaren in the constructors' standings.
Tyre strategy the formula for excitement once more
Much like Bahrain, the excitement generated between Hamilton and Verstappen largely came down to their teams' respective strategical games.
In what was a relatively run-of-the-mill Spanish GP, at the end we suddenly had a Mercedes eating into Verstappen's lead which built to a marvellous crescendo. But the fighting was not just upfront.
The gaggle of cars duelling for a top-10 spot brought some fantastic action, all because different drivers were on different tyre life and compounds, creating racing at a circuit that notoriously discourages such excitement.
Contrast that to the processional Portuguese GP, and Pirelli's role in F1 was highlighted for all to see.
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