For the first two months of the 2017-18 season, La Liga followed a fairly consistent narrative. On 20 fields around Spain, there was no one dominant team. But Atletico Madrid couldn’t score, Real Madrid couldn’t prevent opponents from scoring, and Barcelona was doing just enough of both of those to sneak into a significant lead atop the table.

The Catalan giants led the two Madrid sides by a full 10 points after 12 matches, and appeared to be running away with the title. But they hadn’t been overwhelmingly impressive. They had ridden a bit of luck at the back. There were still questions.

In games 13 and 14, we’re now seeing why there were.

In games 13 and 14, luck reversed itself. Or at least leveled up. In 13, a blatant refereeing error denied Barcelona a clear goal in a 1-1 draw at Valencia. A week later, another errant decision, this time an incorrect offside flag, again hurt the league leaders in a 2-2 draw with Celta Vigo.

But the story that the officiating will obscure is that Barcelona still looks slightly vulnerable. That vulnerability is now being reflected in results.

Valencia deserved its point at the Mestalla, and Celta did at Camp Nou as well. It flew out of the gates, was the better side through 20 minutes, and went ahead in the 20th.

The next 20 minutes, though, were all about Lionel Messi. He was otherworldly. Perhaps the greatest compliment to him is that his brilliance continues to amaze, despite having become the baseline expectation.

He equalized two minutes after Iago Aspas’ opener, and came close to both scoring and creating a second later in the half.

Messi and Paulinho both had opportunities to make it 2-1. Suarez had the ball in the back of the net, but was denied by the flag.

In the second half, both Paulinho and Gerard Pique rounded Celta keeper Ruben Blanco, but couldn’t finish. Suarez, however, did in the 62nd minute after Messi and Jordi Alba combined beautifully down the left:

But Celta was fearless. Marc-Andre Ter Stegen kept the visitors out with multiple world-class saves. But he could only keep them out so often.

He could do nothing with 20 minutes remaining when Aspas beat Samuel Umtiti on the right wing, and the French defender pulled up with a hamstring injury. Aspas was away, and his cut-back presented Maxi Gomez with time and space in the box to fire Celta’s second:

Messi missed an awkward header in the 85th minute that could have capped off a wild early afternoon in style. At times over the final 20 minutes, Celta seemed intent on grabbing a winner. That made for excellent entertainment, and Barcelona very easily could have dropped all three points.

Instead, the league-leaders dropped two. Valencia could pull to within two points of them Sunday at Getafe. The two Madrid rivals could creep back to within six later on Saturday. And the first Clasico of the campaign looms two days before Christmas.

Barcelona still has a significant leg up in La Liga. But its grip on favorite status has loosened a bit. Two consecutive hiccups have left the door ajar.

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Henry Bushnell covers soccer – the U.S. national teams, the Premier League, and much, much more – for FC Yahoo and Yahoo Sports. Have a tip? Question? Comment? Email him at henrydbushnell@gmail.com or follow him on Twitter @HenryBushnell.