Although showing glimpses of their undeniable talent, Alessandro Del Piero, Emile Heskey and Shinji Ono were unable to have a notable impact over the weekend.

Del Piero's flashes of brilliance were not enough to spare Sydney FC from suffering a 2-0 loss away to the Wellington Phoenix, while Heskey could do little to prevent Newcastle Jets falling to a 2-0 defeat to Kosmina's side.

Ono looked sharp in his 30-minute cameo for Western Sydney Wanderers, but the A-League's youngest club had to settle for a 0-0 draw against the Central Coast Mariners.

While a few eyebrows were raised as to why $3.5 million worth of talent did not ignite in the opening round, Kosmina jumped to the players' defence.

The 56-year-old said it was crucial onlookers of the A-League were patient with the competition's marquee icons as they look to find their feet and reach peak fitness.

"You've got to look at the physical aspect or the fitness aspect of the marquees at the moment," Kosmina said.

"None of them have had a full pre-season campaign. They've been doing their training back in their home countries, but it's not the real thing.

"I know our imports (Jeronimo Neumann and Marcelo Carrusca) are actually surprised at the pace, the tempo and the technical and physical aspects of the game in Australia - it's really progressed.

"It's not an easy league to play in, it's a tough league.

"I didn't see that much of the Sydney game but in terms of that one, it's always difficult to go to Wellington and get a result - I don't care who you have in your team.

"Wellington are a hard team to play against over there, real hard team, and I think history proves that point.

"As for Western Sydney, they were very unlucky not to have scored … Matty Ryan (Central Coast goalkeeper) kept them out, and Ono only came on in the game late."

With all three of the marquees having only arrived on Australian shores in recent weeks, Kosmina suggested it would take time for them to assimilate into their new surroundings.

The former Sydney FC coach said it was also important for already established A-League players to adjust to their new superstar team-mates.

"(Newcastle coach) Gary van Egmond made a comment in the paper in Newcastle that the team will have to get used to playing with Emile Heskey," Kosmina said.

"Players that have been together a long time know the nuances of each other.

"I don’t think any of these guys (Del Piero, Heskey and Ono) have been here long enough for that to establish itself."