After helping the Lionesses to a third-place finish in Canada, the 23-year-old quickly found her feet again on home soil.
And her goal helped City clinch a second league victory of the season.
FA WSL 1
Chelsea 4-1 Bristol Academy
Manchester City 1-0 Birmingham City
Sunderland 2-1 Notts County
FA WSL 2
London Bees 1-2 Oxford United
Aston Villa 2-1 Millwall Lionesses
For latest fixtures, results and tables visitwww.FAWSL.com
Duggan, Natasha Harding, Jennifer Beattie and another World Cup star Lucy Bronze all had efforts before half-time but the game remained goalless at the break.
Coral Hines had two good opportunities for the visitors - first a free kick clipped the crossbar, before she shot straight at England stopper Karen Bardsley.
Then Duggan struck on 55 minutes after Lionesses team-mate Jill Scott burst through three desperate Birmingham challenges before cutting-back for the former Everton forward to tap home.
Ten minutes later, Duggan should have doubled her tally, but her shot could only find the side netting, before Nikita Parris was denied by Becky Spencer.
Midway through the second half, Karen Carney - yet another of Mark Sampson's World Cup squad on show in front of over 2,000 fans at Academy Stadium - was denied by Bardsley in the hosts’ goal and City held on for the win.
Meanwhile, Beth Mead’s stunning strike snatched a stoppage-time victory as Sunderland leapfrogged opponents Notts County.
Sunderland defender Hayley Sharp had earlier latched on to Victoria Greenwell’s free-kick at the back post and headed past on-loan Arsenal and England goalkeeper Siobhan Chamberlain to put them in front with two minutes on the clock.
But on 17 minutes, Jess Clarke fired home from 12 yards out to level.
The visitors had thought they had won in the 89th minute, Ellen White again breaking the offside trap but new Sunderland signing Hilde Gunn Olsen was there to deny the England forward with a brilliant one-on-one save
And in time added on, Mead picked up an Abbey Joice pass in the penalty area and fired past Chamberlain with a fizzing, right-footed shot to secure all three points for the home side.
Elsewhere, League leaders Chelsea returned to FA WSL 1 action in style by racking up a 4-1 win over struggling Bristol Academy.
Gilly Flaherty and Gemma Davison put the Blues two up, but Eni Aluko was forced off with half-an-hour gone after picking up a knock. She was replaced by fellow Lioness Katie Chapman, forcing a defensive reshuffle for Emma Hayes’ side.
Ten minutes into the second half Bristol were back in the game when Jade Boho-Sayo slotted in.
Bristol looked close to drawing level but substitute Ji So-Yun was brought down by Frankie Brown in the box, with the Chelsea midfielder converting the penalty to restore the two-goal lead.
And Hayes’ team rounded off the game with a fourth goal nine minutes from time when substitute Millie Farrow beat Bristol keeper Mary Earps to the ball and poked into the net.
There were also two FA WSL 2 games on Sunday as Aston Villa beat Millwall 2-1 and Oxford United won by the same score away at London Bees.
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photos Janos Schmidt