MANCHESTER, England—José Mourinho arrived at Manchester United last summer with the sole mission of restoring the club to greatness. United and its fans had just been through three of their worst seasons in decades, a spell that cost the team tens of millions of dollars, not to mention its old air of invincibility.

But with the Premier League more competitive than ever, Mourinho realized his team wasn’t ready. So in his first year at England’s most storied club, he did what no other elite manager would dare. Right in front of everyone, he openly put Manchester United through a rebuilding season.

It is paying off very quickly. Three games into this year’s campaign, there is an unmistakable menace about the Red Devils. United has swaggered to three straight victories, outscoring opponents by a combined 10-0, and sits alone atop the standings. The club that hasn’t finished in the top three since 2013 is now the British bookmakers’ second-favorite to win the title.

“If the best needed that time, it means the others also need that time,” Mourinho said last winter, recalling that even United’s legendary manager Alex Ferguson got off to a rocky start.

The difference between Ferguson and Mourinho, however, is that United wasn’t the global sports behemoth it is today when Ferguson took over in 1986. Back then, missing out on Champions League qualification didn’t blow a $40 million hole in the following season’s income. And Premier League managers lasted somewhat longer than the current average of 18 months.