England's batsmen scored quickly to chase down the revised target of 101 off 25 overs after England's bowlers, led by Chris Jordan (2-13) and Ravi Bopara (2-31), restricted Afghanistan to 111-7 off 36.2 overs at the Sydney Cricket Ground.
England was aiming to end its tournament on a positive note after being eliminated from quarterfinal contention in a 15-run loss to Bangladesh on Monday.
Ian Bell scored a composed 52 not out and combined for an opening 83-run stand with Alex Hales before Hamid Hassan (1-17) had Hales caught behind in the 14th over for 37, including two sixes.
Bell and James Taylor (eight not out) then safely guided England to its second win of the tournament and perhaps make the flight home a little more pleasant, after stinging criticism from former players and the media this week.
Afghanistan will rue some poor fielding which saw Hales dropped twice at backward point by Najib Zadran off Shapoor Zadran in a nervy opening, as the debutants lost any chance it had of making inroads into England's batting lineup.
Afghanistan, playing at the World Cup for the first time, finished its pool matches with a one-wicket win over Scotland and five losses.Earlier, England started strongly and removed both Afghanistan openers inside eight overs, after winning the toss and bowling.
Nawroz Mangal (4) edged a Jimmy Anderson delivery to Joe Root at first slip in the seventh over and Stuart Broad then removed Javed Ahmadi next over for seven, also caught by Root at slip.
Afghanistan was then given some respite as rain swept over the ground, prompting the players to leave the field for nearly 40 minutes.On the resumption, Jordan had Afsar Zazai (6) caught behind by Jos Buttler.
New batsman Samiullah Shenwari (7) hit Afghanistan's first boundary in the 13th over, but soon after became Jordan's second victim, spooning a catch to England skipper Eoin Morgan at point.
It was Shenwari's lowest score of the tournament, following impressive half-centuries against Scotland and New Zealand and scoring more than 250 runs in total.
Afghanistan reached 50 in the 21st over before rain forced another delay.England again struck in the first over after the resumption, with Bopara teasing Nasir Jamal (17) into an edge to Buttler.
Captain Mohammad Nabi wasted little time getting set before smashing a six off spinner James Tredwell into a group of Afghani supporters in a sparse crowd of 9,000 at the SCT. But Bopara ended Nabi's brief cameo on 16, caught at mid-on, to reduce Afghanistan to 93-6.
Shafuqullah Shafaq top-scored for Afghanistan with 30.