Oval Invincibles 150 for 5 (Capsey 55, Kapp 47*) beat Welsh Fire 111 (Dunkley 56, Smale 3-13) by 39 runs
Winning the toss and choosing to bat on her 35th birthday, Invincibles skipper Lauren Winfield-Hill chopped on first ball of the innings off Shabnim Ismail, not the birthday present she would have wanted.
Capsey countered, hitting Ismail for three consecutive fours. Meg Lanning soon joined the party, timing the ball sweetly against Freya Davies as Invincibles reached 41 for 1 after the 25-ball powerplay.
Lanning fell soon after, sweeping across the line to Katie Levick. However, replays suggested the ball hit her glove before her pad and she'd have been saved if she reviewed.
Capsey was joined by Kapp as Invincibles continued to accelerate. Capsey launched Jess Jonassen for a straight six followed by a slog-swept four, the England right-hander bringing up her 50 from 32 balls. She fell soon after, caught and bowled by the returning Ismail for 55 before Paige Scholfield top-edged Hayley Matthews into the hands of Sarah Bryce.
Amanda-Jade Wellington came out full of innovation, but it was Kapp who held the latter part of the innings together, helping Invincibles reach 150 - a target that felt above par on a surface that wasn't all in the batters' favour.
Dunkley hit the first ball of Fire's chase for four before Matthews twice found the boundary in the first 10 balls of the innings bowled by Kapp.
Dunkley then hit Rachel Slater for four boundaries before Matthews found the rope off Sophia Smale. But the West Indies star fell to Wellington for 12, perfectly picking out Phoebe Franklin in the deep.
Kapp (2-24) returned and struck twice in two balls, getting Tammy Beaumont lbw for 5 before clean-bowling Georgia Elwiss. Jonassen was then caught at mid-off off Capsey (2-16), Fire in trouble at 67 for 4 with 84 still required from 48.
Dunkley brought up her half-century from 36 balls, Fire's first of this year's competition, but Bryce fell from the next delivery to further worsen their position. With 30 balls remaining, Fire still needed 61 and when Dunkley finally fell for 56 from 41, with her went the Fire's chances.
Kapp, the Meerkat Match Hero, said: "We didn't start off this tournament like we wanted to, but it feels like we've got a bit of momentum now.
"We started the same way last year, in the first two games we probably weren't too far off our best and luckily it looks like things are improving.
"It was a different pitch to what we're used to playing on here at The Oval. Capsey's innings was brilliant and she allowed me to knock it around and get myself in. It's good signs if we can adapt on different wickets."