The Witcher 3: Wild Hunt

In the beginning, if you are in the first inn, there is a person who will teach you the card game. After the lesson you can play against him again and try this achievement like me, it's pretty easy with the cards from the start:

You have to win a round of Gwent with only using neutral cards like Zoltan Chivay. You will gain Zoltan as the first neutral card after defeating the man in the first inn. It isn't necessary to win the first game. You can earn it in a rematch, too. Nonneutral cards have a blue sign on the left side and can be played in every deck.

In the first round, try to play many cards, but not Zoltan Chivay, with a high attack so that the opponent have to (and he will) play all his cards to win this round. I tried it often and it worked nearly everytime. It can still be, that you have to try it a few times because I did this a few updates ago and the behavior changed through a few updates.

Now that he has no more cards to play it's very easy to win with playing only Zoltan. Even if he has a card to lower his attack.

This solution depends on a little bit of luck that you have many cards with high attack stats in your hand. And don't try to play too many cards. The enemy will give up the round if he can't play enough cards to win this round, so begin with the lower ones.

Good luck, I hope this will help to get the achievement!!

Edit: If you have completed the area and the man who taught you the game is gone, I would start a new game, maybe, if you didn't do it already with a harder mode for later (Please pay attention to my second Edit!). It tooks only 10 minutes or so to get to the man (tutorial while Gerald is dreaming, first encounter, second encounter and you're in white orchard. I don't know if there is someone else who's easy to do this achievement, but I played almost against everyone in Velen and everyone is much harder then the man in the beginning, because they have many cards with a high attack and they won't play all cards in the first round. So I would start a new game!

Edit 2: In the further game there are many player who are very easy, too. So it isn't really necessary to start a new game! But it could be a faster way if you need an achievement for the streak.

Edit 3: If you vote negative for my solution, then please give me feedback! Thanks.

If you missed the opportunity to nab this during your first "intro" game of Gwent at the inn within White Orchard, I've got a method to help you out.

It's a matter of circumstance but hopefully this guide will make you aware of what to do, when it happens. I had actually unlocked it by chance and realized after what I'd done, so I thought I'd share.

Must have the Heart of Stone DLC for this solution.

When you first arrive in Velen you can buy the Gaunter O’ Dimm card. The merchant at the elven circus has two. He is located northwest Carsten, and west of the Vegelbud Residence.

Then travel far to the Northeast to the merchant at the windmill. He will sell you an additional Gaunter O’ Dimm. The card has the “muster” ability. Which means when you play one, it will play all three and give you a score of 12.

Similar to other solutions you can lose round 1 and make your opponent use up their strong cards. Use just Gaunter O’ Dimm in the second, hopefully the opponent passes. Now win the 3rd round.