The heavy sack pushed Chapman's two-day total to 43-9, and he said he caught numbers of quality fish today (June 8).
"I threw back a 17- to 18-pound stringer today," Chapman said of his day on the water.
Matt Herren sits in second with 42, first-day leader Cliff Pace slipped to third with 39-12, Casey Ashley is in fourth with 39-3 and Ott DeFoe rounds out the top five with 38-2.
Gonzales' Greg Hackney moves into the third day of competition in 10th place with 34-10.
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Chapman said he caught all of his fish the past two days on a single point, working the thermocline.
"It's been hot, the water's hot, and they're in their summer pattern," he said. "The thermocline is at 30 feet, and they are literally right there at it; they want to get as deep as they can."
He was mum on exactly how he caught the fish, but he said he felt confident there will be plenty of fish left to carry him to the final-day cut.
"I caught about 20 fish both days," Chapman said. "I also backed off of it halfway through the day (today) and tried not to beat it up."
He said he hopes he finds the fish stacked on the tapering point tomorrow because he hasn't been able to replicate the pattern since finding the spot on the last day of practice.
"It's not a pattern because I spent the rest of the (last practice) day looking for similar stuff and couldn't find it," Chapman said.
Herren, who entered the second day of competition in sixth, said he is fishing two ridges he located at the very end of the final practice day.
"I caught 100 fish yesterday," he said. "Yesterday, I had to go through so many fish trying to find out what's going on."
That work, however, allowed him to key on tactics that today produced bigger fish more consistently. He said he's fishing three baits, rotating through them.
"I'll get them going, and catch a few," he said. "It's just typical offshore fishing."
He said there should be plenty of fish left for the final two days, if he can make the top-12 cut tomorrow.
"It's the kind of place that will reload (with bass)," Herren said. "Whether it'll reload with big ones, who knows?
Only the top 50 anglers fish tomorrow, with the resulting top 12 pros moving on to the final day.
Blast-offs and weigh-ins will be held at Cypress Bend Marina, and are free and open to the public.