The St Helens and Great Britain rugby league winger lines up for Wales A against Argentina at Pontypridd with just four hours' union experience to fall back on.
However, the first three appearances - and three tries - in the blue and black of Cardiff on a three-month contact have proved enough for the Welsh selectors.
"It is a big occasion for me," admitted Sullivan. "It will be a step up, but it's a level of rugby I am used to playing in league.
"I am learning all the time in union. Every game provides something new, so I've got to be on the ball each time I play.
"I'm thoroughly enjoying it with Cardiff and I'm gradually picking up the union moves," he said.
Sullivan touched down twice on his debut in Cardiff's 90-point rout of Cilfynydd in the Welsh Cup, then impressed the watching Wales coach, Graham Henry, when he scored a try against West Hartlepool.
Henry toyed with the idea of fielding Sullivan against South Africa last Saturday before deciding against it. "Anthony is a marvellous prospect for the future of Welsh rugby - he has many positive attributes," Henry said.
"When I saw him in the West Hartlepool game he looked twice as quick as anyone else on the pitch and, whichever way you look at it, there is no substitute for pace.
"It is only a matter of time before he gets a greater feel for the 15- man game."
Sullivan will take his place alongside 10 internationals as Wales's second string look to continue the momentum generated by the senior team's outstanding performance against the world champions.
That heroic Wembley display has clearly made it tougher for those players on the Test team fringes to break through but several individuals will have one eye on this season's Five Nations campaign, which starts for Wales away to Scotland in under three months' time.
Winger Wayne Proctor, scrum-half Paul John, hooker Garin Jenkins, lock Ian Gough and No 8 Nathan Thomas are among those with points to prove after being overlooked for the Springboks Test.
Geraint Lewis may yet find himself in the Test team. That depends on the outcome of Scott Quinnell's appeal hearing. If the Pontypridd flanker is withdrawn from A team duty Neath's Scott Eggar will take his place.Reuse content