You can throw out the old book on GM Anish Giri. He's writing a new one here at the 2015 Qatar Masters Open.
"So far here with Black I'm playing like I like as White," Giri said after the game between the top two players in the world.
For those that wondered if his first two trips with the Najdorf were just a sideshow against lower-rated players, today the answer came: he will use his new weapon against anybody. Giri neutralized World Champion Magnus Carlsen's turn with White, and while the draw didn't get the Dutchman closer, it did keep him within striking distance and allowed two members of the chase group to climb atop the tables.
"I played the Berlin for I don't know how long," Giri said. "I never played the Najdorf in my life...I think I'm playing it quite well in the games that I've played here, which is very surprising. I have no idea why."
He's explained that he's been sitting on the opening knowledge for a while, waiting for the opportunity to use it.
"I've done of course a lot of work on it throughout the years. I've just never gotten to play it. Whenever I wanted to play Nadorf people would go 1. d4 and that would happen 20 times."
Despite the recent success, he still holds fondness for his bread-and-butter defense: "Najdorf is a great opening, when it works. Other times you pay for it. The Berlin is always a great opening."

Some parts of Qatar received up to 25mm of rainfall on Friday's rest day, but that didn't lead to many storms on the top boards when action resumed at the 2015 Qatar Masters Open.
After a draw between GM Wesley So and tournament leader GM Magnus Carlsen on board one, eight players on boards two through five had a chance to erase the margin with the world champion. All failed to do so, with each of the games ending drawn. Of that octet, GM Anish Giri came the closest.
Let's start by looking at the super-GM matchup at the top of the tables. So played Carlsen for the fourth time in 2015, after never having played him before this year began.
The American held his own in the first two contests before falling victim to a very Carlsen-esque squeeze at the Sinquefield Cup. Today the Berlin airlifted somewhere else -- the now-dominant system against the Ruy Lopez took a backseat in several games to variations of the Closed Spanish.
Once the center pawns traded, the players didn't strive for much and agreed to terms in a level position. On the final move, Carlsen can even trade off his only "weakness" with 39...d5 if he had so desired.

If the opening rounds of the 2015 Qatar Masters Open resembled cat-and-mouse with lower-rated opposition, so too did the beginning of World Champion GM Magnus Carlsen's fifth-round game. He waited and waited for ...Be6, then pounced with Nf4 and went full-on tiger against Black's king.
Playing GM Li Chao for the first time, the Norwegian knew he would face a Grunfeld but didn't know the game would explode like it did. Both sides threatened various mates on opposite rook files, with Carlsen offering a pawn to expedite his attack, while Li Chao offered his whole queen!
Carlsen had it mostly worked out, even avoiding an aesthetic but faulty pitfall -- a mouthwatering underpromotion that actually would have mated himself! Instead he went for a more practical win, and with it he earned sole possession of first place as the tournament takes its only rest day tomorrow.
"Today I felt like playing a sharp game," Carlsen said when he saw the "red flags" in Li Chao's position. "Once in a while I feel up to the challenge. It was a very strange struggle at first. We were both making waiting moves. When I had the chance I just went for it. I don't know if it was correct by any means."
Did he agree with GM Vladimir Kramnik's statement that it's easier to play against 2700s since their style is more expected?
"Maybe, but also playing through Li Chao's games before the round today, I realized that I don't understand the way that he plays at all."