Nikon recently stated that high end DSLR sports camera are still superior but this might not be true anymore:

The new Sony A9 5.0 firmware has been tested by Tony Northrup. He now states the A9 AF tracking is better on the Sony A9 than on the Nikon D5. Mirrorless finally did beat DSLR in their last bastion.

And here two more videos:

Sony a9 video tracking fix

Sony a9 Firmware 5.0 Menu walkthrough

Finally Sony learned the leasson from Fuji’s camera support philosophy and released their best firmware update to date. This adds a ton of features and fixes for the A9 making it become a sort of A9II :)
But they key here is the new autofocus system which simply works like a charm. Here are a few examples but please feel free to add your test in the comment system!

And a discussion about the new fw upgrade: