Merimbula won the toss on Saturday and opted to bat first on their home field, with openers Matt Lawson and Brendan Daley laying the foundations for their innings.
Daley clocked in 41 runs before he was caught out by Hamish Willcox, while Lawson was on 26 when Wilcox clean bowled him.
With the top order dealt with, catches to Willcox and Chris Dwyer provided some cheap wickets and the hosts looked in danger.
A middle order stand regained some control, but when Ash Postance was caught behind by Geordie Gibbs, the Merimbula batting line-up crumbled easily.
Gibbs snagged another catch off the bowling of Adam Blacka when he took Zac Wells for just two runs.
Jay Richmond was defiant of his Tathra oppressors, holding down the crease to score 24 not-out.
However, the Knights ran out of overs as they notched up 6/139.
Pete Bennett provided impact for the Tathra side, bowling medium pace, he claimed three scalps on the day for just 22 runs.
The reply from the Sea Eagles was swift as the visitors gave up just two wickets while chasing down the target.
The Sea Eagles were more aggressive at the crease, actively chasing runs as they locked in the win after just 26 overs.
Pete Bennett was in complete control as he knocked 77 runs.
In other matches, the Bluedogs claimed a comfortable win over Bermagui with Liam Allan forming the basis at the crease, hitting a half-century.
The Bluedogs will host the Knights this weekend at Pambula from 1pm Saturday.