Adm Thad Allen said 6,000 barrels of oil were captured in the first 24 hours after the procedure commenced on Thursday.
This represents between a third and a half of the estimated daily leakage since the Deepwater Horizon rig exploded and sank on 20 April, killing 11 workers.
Adm Allen said BP hoped to increase the amount captured in the next few days.
Speaking in Theodore, Alabama, he said the company was able to bring up 6,000 barrels of oil from the well in the "first full 24-hour cycle".
Asked if the proceedure was working, he said: "Yes, with caveats."
Adm Allen added that it was hoped that a higher collection rate could be achieved by closing vents in the containment cap over the next few days, as engineers managed to stabilise pressure in the well.
On its twitter-feed, BP stated it had captured a total of 6,077 barrels of oil on Friday.
The new figure exceeds rough estimates made on Friday suggesting the cap was funnelling the equivalent of 1,000 barrels a day .
Adm Allen also said that winds had pushed the slick closer to about 200 miles of coastline stretching from the Mississippi-Alabama border to Port St Joe in north-west Florida.
Both BP and the US government have faced criticism over the spill, which has been described as the biggest environmental disaster in US history.
In his weekly address on Saturday, US President Barack Obama promised to use all resources within his means to clean shores and help those whose livelihoods had been affected.
He also said he would ensure BP would be financially accountable for the spill and that the company would pay out "every dime" they owed.
He met residents of Louisiana on Friday, his third visit since the spill began.
BP is also digging two relief wells which it hopes will provide a permanent solution to the leak - but they are not due to be completed until August.
The estimates for the total amount of oil that has leaked since the spill began vary widely from 20 million to 45 million gallons.