Saracens boss Mark McCall was delighted by both Mako and Billy Vunipola in the 42-20 win over London Irish at Twickenham.
Billy made his first start for Saracens after joining from London Wasps over the off-season.
Having won his first two caps for England against Argentina in June, the number eight has now linked up with his brother Mako and started at blindside flanker against the Exiles.
Loosehead prop Mako, who went on tour with the British and Irish Lions and started in the Test series against Australia, scored a try after coming on as a replacement in the second half.
Pleased by the performances of both players, McCall emphasised the need for Billy to keep improving, having already slimmed down during pre-season.
"You can see their quality on the ball and in that second half things opened up a little bit," said McCall.
"You give Billy and Mako time on the ball and things happen around them. Mako is a decision maker on the ball - when to offload and when not to, he never makes errors.
"Billy was great out there, part of a good back row. He can do very well for us and will play number eight regularly, but he can play a few positions.
"The one thing Billy has done since he's come to the club is learn to work hard. He's lost some weight over a short period of time, the type of weight you want to lose.
"He's in the best shape he's ever been in and that's transferred on to the pitch. Hopefully his work ethic will continue.
"Billy has spent his whole life running over and through people at his own age group. To go to the next level he must work hard."
England winger Marland Yarde was a rare highlight for Irish on a tough afternoon, with boss Brian Smith praising his impact on the match.
"Marland's performance speaks volumes. He was probably the standout winger and is a very, very good player," said Smith.
"If he keeps his feet on the ground and keeps working hard...Marland's biggest strength is his massive desire to improve.
"He has guys around him in the changing room who can help him go through the transition from rookie to actually being on the radar. There's no doubt he's a very good player with a massive future ahead of him."