Chisnall, in his first match at the competition since replacing Phil Taylor alongside Adrian Lewis, threw the winning dart as England won 5-2 to set up a second-round tie against South Africa.
Dyson Parody and Dylan Duo of Gibraltar had their moments but each missed a double to crucially slip 3-1 behind.
A double five from Parody was Gibraltar's highlight, but with both sides then needing to check out from 20, Chisnall nailed the vital shot for the No 2 seeds.
England are aiming for their fifth World Cup trophy in seven attempts.
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Third seeds the Netherlands, with Michael van Gerwen and Raymond van Barneveld in tow, coasted past the Czech Republic.
Van Gerwen was hobbling on an injured foot and grimaced after every throw but the two-time World Cup winners still won 5-1.
Host nation Germany whipped the crowd into a frenzy after beating No 6 seeds Northern Ireland 5-4.
Martin Schindler and Max Hopp, both just 20-years-old, held their nerve to edge their far more experienced counterparts Daryl Gurney and Brendan Dolan.
Brazil's popular debut at the competition began brightly with a 5-4 win against Switzerland, teeing up a second-round tie against Germany.
Brazil's Diogo Portela said: "When I made the move [from Brazil to England] three years ago I never imagined [success] it would come so quick.
"The hardest thing I've done was to leave my family and friends behind. Now, playing darts, is easy."
Friday's first-round results:
USA 5-1 Italy
Canada 5-2 Hungary
Austria 5-0 China
South Africa 5-3 Sweden
Brazil 5-4 Switzerland
Northern Ireland 4-5 Germany
England 5-2 Gibraltar
Netherlands 5-1 Czech Republic
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