Winning start for young LionsChopper also had praise for three of his players in particular, adding: "Tom King, who was formerly with Crystal Palace, played in goal and gave very good account of himself.
"Overall it was an excellent win. The boys worked extremely hard after what has been a very long pre-season. They got their reward today, everything they have learnt with us and Ollie and Birch - it all came together. I am very pleased for them, they deserved that win."
"Dylan's was a 35-yard volley that he hit sweetly," said Chopper, "But Alfie's goal was just as good because it was scruffy, centre forward's goal that came from closing down the keeper. He had a bit of fortune but a lot of desire and got our second goal because of that.
Pavey put the result beyond Barnsley's reach two minutes after the break, sliding home from close range. Although not as spectacular as Casey's effort, Lions coach Neil Harris believed both goals were excellent in their own way.
Casey's opening goal after 25 minutes was an outstanding strike, catching the ball fully from 35 yards out and sending an unstoppable volley into the top corner.
Millwall U21s got the new Professional Development League 2 season off to a flying start as goals from Dylan Casey and Alfie Pavey secured a 2-0 win at Barnsley on Monday afternoon.
"It has been hugely beneficial for the lads getting time with Ollie and Birch to learn how the first team are playing. It always take the younger boys longer to adapt as naturally seniors learn quicker, but it is very pleasing for us all to see it come to fruition as it did today and follow on the seniors' win at Fulham on Saturday with an opening day victory ourselves."
Millwall:King, Siafa, Goodman, Wood (Parr, 55mins), Casey, Powell, Thompson, Philpot (Bryon, 68mins), Pavey, Farrell (Rylah, 60mins), Webb. Subs not used: Girling, Peter.