Cassel can't repeat the three interception meltdown he had in last week's 27-20 loss to the New York Giants if the Cowboys (2-4) have any chance of ending their four-losing streak.
But the Cowboys saw competitiveness in Cassel they hope to build on.
"Absolutely, I thought you saw that within the game," coach Jason Garrett said of Cassel's competitiveness. "I thought he did a really good job overcoming some of those mistakes. He played a good football game and made some bad decisions that impacted the game but the drive that he had at the end of the ball game I thought was big.
"To lead the one drive to tie the game and then to give us a chance at the end after that, he is a tough guy, a mentally tough guy. I think the guys see that. Just love how he competes. Love his relentless spirit and his fight."
Garrett said it was good for the Cowboys see Cassel's competitive fire considering their limited history with him. He was acquired on Sept. 14 in a trade with the Buffalo Bills.
"I don't know if they know a lot about me, but I'm always going to fight for them," Cassel said. "And I think they saw a little bit of that. No matter what the circumstance is, I'm not going to hang my head and be one of those guys that are going to sit there and mope around and just wait for the game to end.
"I'm going to fight until the end no matter what the circumstances, no matter how had they got at times, and try to continue to put ourselves in position to win the ballgame."
Cassel has three games with three or more interceptions in his last eight starts dating to 2013 and 2014 with the Minnesota Vikings.
But what's also true is that remains the Cowboys' best hope to win until starter Tony Romo returns from a broken collarbone on Nov. 22.
Despite the interceptions, Cassel helped open up the offense with the big play.
The Cowboys had six plays of 20 yards or more compared to six combined over the previous three games with quarterback Brandon Weeden at the helm.
Still he's not resting on sleeping on his successes. He is working to remove the mistakes.
"You know what? That's the most important part," Cassel said. "I lost a lot of sleep over it and everything else. I'm just disappointed that it went the way it did because I think offensively, for 90 percent of the game, we played well enough to win.
"And then you have those three interceptions, and it really dictates the outcome of the game. That's what's hard to swallow. And as a quarterback, you beat yourself up over it. You say, 'What can I do differently?' You learn from it and then you come back the next week and get stronger."
Cassel and the Cowboys believe he should be better in his second start because of the added comfort in the offense and rust factor. The Giants game was his first extended playing time since October of 2014.
He didn't play the final 13 games of the season. And although he was credited the start in the 2015 season opener against Buffalo, he was in for only one play and didn't throw a pass.
"That may be part of it too," Cassel said. "Again I'm not an excuse guy. But at the same time it has been a while since I have taken a few hits.
"It was great to wake up on Monday morning to feel that soreness and be in the game again. I will be better this week. And I promise to work as hard as I can to be better this week."
SERIES HISTORY: 17th meeting. Dallas leads the series 10-6. Dallas has won four of the last five, including three of the last four in Dallas. A Dallas win would snap a four-game losing streak, the longest of coach Jason Garrett's career.
GAME PLAN: The Cowboys need to stop the run and forced quarterback Russell Wilson to win with the Seahawks' suspect passing game and injury ravaged offensive line. The Cowboys believe they can get pressure on Wilson with defensive ends Greg Hardy and Randy Gregory. They have to get him obvious passing situations. Offensively, the Cowboys will lean on running back Darren McFadden to set up the play-action passing game. Quarterback Matt Cassel needs to avoid the turnovers that plagued him in his first start.
--Seattle RB Marshawn Lynch vs. Cowboys LB Rolando McClain.
Lynch is going beast mode again. He had his first 100-yard game of the season in the Seahawks' 20-3 victory over the San Francisco 49ers, gaining 122 yards and scoring a touchdown on 27 carries. Seattle will be leaning on him against the Cowboys, who have allowed more than 100 yards rushing in each of the last four games, all losses. But the Cowboys have allowed only one individual 100-yard rusher, Atlanta's Devonta Freeman, who had 141 rushing yards. McClain struggled against the run against the Giants last week and will need to hold firm if the Cowboys are going to contain Lynch.
--Seattle CB Richard Sherman vs. Cowboys WR Dez Bryant.
Dez Bryant is expected to play for the first time since the season opener and the Cowboys need him to be a playmaker on the outside to open up the running game. Bryant is the only player on the team who can win one on one battles. Of course, doing that coming off and injury against Sherman will be a tall order. Bryant had four catches for 63 yards against Seattle last year.