South Africa's top-order may not have fired but skipper Graeme Smith is happy that the middle-order made up for it in the Proteas' comprehensive win over Ireland that sealed their quarter-final spot in the ongoing World Cup in Kolkata.

After a shaky start, South Africa's middle-order and bowlers responded strongly to beat minnows Ireland by 131 runs at Eden Gardens on Tuesday night. The Proteas thus became the first team to qualify for the knock-out stage from Group B.

"It's fantastic to qualify from the tense group. Each team is getting ready for the big stage so it was nice not to be caught up with the tension. The mindset is to win and we have to keep up with the winning habit," Smith said.

The Proteas made a wobbly start after being sent in to bat as their top order collapsed in the absence of leading run-getter AB de Villiers, who is down with a thigh strain.

- Scorecard

But sensible batting by the left-handed duo JP Duminy (99) and Colin Ingram (46), who were engaged in an 87-run partnership for the sixth wicket, led the fightback.

Asked about his reaction on the middle-order's performance in the last two games, where they bailed out South Africa from tricky situations, Smith said, "I see this as a positive as the guys have responded well to the situation. JP (Duminy) held on the innings. It was also great to see (Colin) Ingram getting some runs under his belt.

"Now we can look forward to the game against Bangladesh. It's going to be a different soil in Bangladesh," he added.

Smith said he was not concerned about South Africa's likely opponent in the quarter-finals.

"It really does not matter who we meet in the quarter-finals. It's about winning and I'm happy that the boys are winning now.

"As I've already said this group is really unpredictable. It all depends on who plays well on that given day," he said.

- Images: SA thrash Ireland to reach QFs

He is still waiting for the big knock from his own bat and Smith said, "As of my form, I'm working hard and looking forward to some good runs. You can't help when you are caught in yes and no calls for a run out. Hopefully, I'll score some runs in the match against Bangladesh."

Having missed out on a century, man-of-the-match JP Duminy, who got out on 99, said, "I was not disappointed at all. I was looking to get as much runs as possible. In the end it's all about the team.

"It was not the usual Eden pitch and was a little up and down. We thought anything around 250 will be a decent score on this ground," he added.

"I would not say it's my best but one of my better knocks and I can get a lot of confidence from the knock."