The 49ers lost to the Texans, 24-13, in their exhibition opener on Sunday.
But San Francisco's defense held Houston to 89 total net yards in the first half.
"Really fun to watch, really aggressive," Greg Cosell, Senior Producer at NFL Films, told KNBR 680 on Monday. "I loved both corners. Jimmie Ward was terrific playing press corner; Brock was good. It was a fun defense to watch.
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"The linebackers played downhill with aggression ... I really enjoyed watching the defense."
The 49ers selected Ward in the first round of the 2014 draft.
He appeared in eight games as a rookie, and all 16 (eight starts) last season.
[REWIND: O'Neil: Ward one of 49ers' top 11 defensive players]
San Francisco 49ers
"I remember talking to Jim O'Neil at the combine ... he told me how much he liked Jimmie Ward then," Cosell explained. "I think he was thinking more in terms of safety then, but obviously they made the transition to corner. Now Ward played both coming out of college ... I loved watching him play press. I thought his technique overall at corner was very good."
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What aspect of the 49ers' defense concerns you the most?
"I'd say pass rush, which is obviously critical," Cosell answered. "The reality is pass defense in the NFL is a combination of pass rush and coverage. And the less you can get to the quarterback, the greater strain it puts on your coverage no matter how good your secondary is. And it works both ways...
"I think that we're still looking to see where a consistent pass rush will come from, particularly out of their nickel package ... they need some edge rush ... you can always scheme pass rush but you don't necessarily want to make a living doing that. Now Jimmy O'Neil has great background in scheme rush because he's from the Mike Pettine-Rex Ryan group ... but you'd like to be able, at times, to just win. Have people win off the edge or inside."
The 49ers will be without Aaron Lynch -- arguably their best pass rusher -- for the first four games of the season.