Australia beat India as women's cricket makes Commonwealth Games debut
Chasing 155 to win in the 20-over game, Australia were in trouble at one stage having lost half their side for 49, but Gardner got them over the line in style with an over remaining.
She smashed nine fours in her 52 not out off 35 balls while Grace Harris chipped in with 37 off 20 balls before Alana King (18 not out) helped finish the job.
India bowler Renuka Singh took 4-18 in her four overs but the effort was in vain.
India had opted to bat first after winning the toss and made 154-8 in their 20 overs thanks to skipper Harmanpreet Kaur's 52 off 34 balls - a knock that included eight fours and a six - as well as opening batter Shafali Verma's 48.
But Jonassen's 4-22 meant that the lower order could not take them to a bigger total.
Early Group A leaders Australia face Barbados on Sunday while Pakistan meet arch-rivals India.
Cricket is returning to the Commonwealth Games after a 24-year absence with the women's tournament.
South Africa's men's team won the gold medal in the 50-over competition in Kuala Lumpur in 1998.