The improved defensive effort came in the absence of captain Ron Vlaar, Philippe Senderos and Nathan Baker prompting suggestions from Lambert that his job will be difficult once the aforementioned trio return from injury.
"Our defensive effort was terrific at Selhurst Park," said Lambert.
"For Okore it's his third game in quick succession, and he's been out for more than a year. And I think Ciaran Clark certainly: the two of them have certainly stepped up their game.
"That's the aim of football, to have selection conundrums, and those two are going to give me that when others return. You have to push a mate to get into a side, and at the minute these two lads are holding their own."
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