The head coach was delighted with how his players dealt with the 'mental challenge' of being in the field under a hot sun all day, as the home side moved from their overnigh 88 for two to 394 for four.
Sam Hain scored 140 not out from 337 balls while skipper Will Rhodes made 99, with the Bears ended the day still 203 runs in arrears in reply to Northants' mammoth first innings scored of 597 for six.
Jack White was the pick of the Northants bowlers as he claimed two for 84 from 26 overs, while the only other wicket to fall on the day was taken by Luke Procter, who ended with miserly figures of one for 19 from 16 overs.
It was undoubtedly a tough day, and 55 overs of spin have now been bowled by Northants without a wicket being taken.
"All credit to the lads," said Sadler. "On days like that it is a mental challenge and they kept going and were super.
"The bowlers were good with funky fields and they tried different bits but the pitch is pretty dead now.
"There was the occasional turn off the straight but it didn't really turn out of the footholds.
"It was a tough day but they kept toiling away and kept trying.
"I can't fault them for effort, we were still buzzing and there was still a presence in the field and some noise and they were still running round and diving and all credit to them."
Sadler also had some special words of praise for White, who is making his first Championship appearance of the season.
"Jack White was great," said the head coach. "He's been bowling well all year and been a little bit unlucky not to play any cricket so far for us.
"But we are a squad and he has got his chance this game and come in and bowled beautifully.
"He made a couple bounce and got a couple of wickets and I can't fault him."
Warwickshire batter Hain also had some words of praise for the Northants attack.
"I thought we grafted really well," he said.
"I was really pleased for Rhodesy and to see him back in some runs.
"He played fantastically because credit to Northants, they bowled really well on a wicket which was flat at times but showed that if you put the ball in the right area it did enough to give the bowlers some help.
"I am pleased with the way I and the other lads played to show the resilience we needed after Northants had got nearly 600."
Day four will start at 11am on Sunday.