Which top GMs have poor opening knowledge?

Can GMs get by with only basic opening knowledge? 

"... With his superb intuition and depth of positional understanding, [Petrosian] was accustomed to treating the opening relatively flippantly, and did not normally strive very hard to gain a theoretical advantage. … It must be remembered that, despite its shortcomings, Petrosian's approach proved good enough to wrest the world title out of the hands of Botvinnik, one of the best-prepared players ever. ..." - FM Steve Giddins (2003)

In today's game, it would be impossible for someone to become a "top GM" without having extensive opening knowledge. Even if someone were the best in the world after getting out of book, having poor opening knowledge would put them into losing positions time and again when playing the best in the world. 

You would be amazed at how much opening knowledge even "mere" IMs have. Even when they are not doing opening prep, these guys look at dozens of GM games every month, so they absorb opening knowledge almost by osmosis.

It's relative.

The best prepped lines of most 2200 players wouldn't be as thoroughly prepared as some of the worst lines of top GMs.

Top GMs have been in the game in a professional capacity for so long that, as the saying goes, they've forgotten more about chess than you've ever learned.

So no, it's basically impossible for a GM to have "poor" opening knowledge in the sense that most amateurs will use the word "poor."

The quotation about Petrosian is a bit misleading. Petrosian was theory for the pet lines he played over and over again. He knew and understood the typical positions as well as anyone in the world

The word, "theory", is not in the quotation. The quotation does mention "his superb intuition and depth of positional understanding".

Magnus Carlsen says he plays by intuition  most of the he spends thinking were simply double check what a liar. 

This idea that some top GMs have "poor opening knowledge" is simply garbage. Magnus Carlsen me claim that he plays by "intuition," but that so-called intuition has been honed by playing over thousands of top level games and reading over tens of thousands. He had an incredibly deep knowledge and understanding of all the major openings. All the Super-GMs do. 

"The knowledge of variations is, after all, only a sham." - Richard Reti

The quotation is false. Get rid of it.

Is there a reason to believe nighteyes1234 instead of FM Steve Giddins?

None, of course. However, now and then they are caught off guard. Remember when Anand lost a game in seven moves, for example.

All relative at that level, of course, but when Gata Kamsky was E2700+, the opening was considered the chink in his armour.

Actually six

Actually, Anand lost to Zapata in 6 moves because he had studied his opening theory! He came across the game Miles - Christiansen 1987 in the Informant and saw that Black had achieved a quick draw, so he played the same line. What he didn't know was that Miles and Christiansen had agreed in advance to draw their game. When Ckristiansen blundered with 5...Bf5, Miles rubbed the e2 square with his finger to show Christiansen that he had blundered, but he honored their draw agreement. Poor Vishy saw the game and innocently repeated the line without checking it. If he had known a little less theory, he probably would have figured out that the move was no good

There's Granda Zuñiga.

Granda Zuñiga.

I said it first