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Ding trailed 4-1 in the best-of-nine-frames match when he made his clearance, but world number three Robertson recovered to win 5-2.
"The reds were looking good so I went for it," Ding told BBC Radio 5 live.
"It's just a 147, a new record for me. I like to beat the records every time I play in the tournaments."
Robertson, who made a 140 break in the third frame, praised his opponent saying: "What a wonderful break.
"He was clearly determined because he went for a risky shot in the forties."
Ronnie O'Sullivan turned down the chance to make a 147 break in the first round because the £10,000 prize money was "too cheap", making 146 after choosing the pink over a black.
The £10,000, which is boosted by £2,000 on offer for the highest break of the tournament, is a rolling prize fund at ranking events.
O'Sullivan thrashed world number one Mark Selby 5-1 in his quarter-final on Friday, and insisted he had been trying for a 147 when an opportunity arose.
"I thought 'he's let the lads down, hasn't he?' O'Sullivan joked when asked about Ding's maximum.
"Ding got it. Fantastic, at least they've had a 147 this week - and a 146. But I was going for it, 100%. There's obviously pressure and I twitched on the black."
Despite making headlines for his decision to ignore a possible 147 earlier in the week, O'Sullivan added: "I think I've done brilliant for this tournament.
"Most people are saying they didn't actually know this event was on. I've created such good headlines - if you had to go and buy them headlines, it would probably cost you a few quid.
"They've had the best of both worlds. They've had a maximum from Ding, they've had the headlines from me this week, so I think I've given great value for money."
After losing only one frame against Selby, a relaxed O'Sullivan said he was in the mood to "go for everything" and entertain the crowd.
"That's exactly what I was thinking, it's good practice for the exhibitions," said the Englishman. "If you start to think of it like a match you can start to not enjoy it.
"It's not really that important. Although it's nice to win and you want to do well, don't get me wrong."
O'Sullivan goes on to face compatriot Joe Perry, who beat Ben Woollaston 5-1, while Robertson will play Northern Ireland's Mark Allen, who beat Michael White 5-0.
China's Ding Junhui made a maximum 147 break in the quarter-final of the Welsh Open in Cardiff but could not beat Australian Neil Robertson.