Around 50,000 English and maths GCSEs were awarded the new highest grade this summer, amid the biggest shake-up of exams in England for a generation.
Just over 2,000 teenagers in England scored a clean sweep, gaining 9s in English, English literature and maths.
Overall pass rates fell, with around a fifth of entries in England, Wales and Northern Ireland achieving at least an A or 7 under the new system, while two-thirds gained at least a C or 4.
Under the overhaul, traditional A* to G grades are being gradually replaced in England with a 9 to 1 system, while courses are being beefed up with more demanding content.
English and maths, key GCSEs for all teenagers, are the first to move across, with other subjects following over the next two years.
Statistics published by the Joint Council for Qualifications (JCQ) show that among 16-year-olds in England:
:: In maths, 3.5% of entries, around 18,617 in total, scored a 9
:: In English, 2.6% of entries, around 13,754, scored a 9
:: In English literature, 3.3%, around 17,187, scored a 9
:: Girls secured more 9 grades than boys.
Across all UK entries for the new courses, around 50,700 achieved a 9.
Fewer candidates achieved a 9 than the proportion who gained an A* under the traditional A*-G grading system, following the deliberate move to change the system to allow more differentiation, particularly between the brightest candidates.
There are now three top grades, 7, 8 and 9, compared with two under the old system, A* and A, with A* results now split into 8s and 9s.
The grading switch is part of wider reforms designed to make GCSEs more rigorous and challenging.
Maths in particular has more content, and in both subjects there has been a move away from coursework and pupils now sit all exams at the end of the two-year courses, rather than throughout.
Although the exams have been made more demanding, broadly the same proportions of candidates have achieved key passes, such as at the A/7 boundary, due to processes put in place to ensure that results are comparable and that students taking the first new courses are not disadvantaged.
Data published by exams regulator Ofqual shows that among 16-year-olds in England, 19.9% of maths entries were awarded at least a 7 or higher this year, compared to 2016 when 20% achieved an A or A*.
In English language, 16.8% scored at least a 7, compared with 16.2% who gained at least an A last year, while in English literature, 19.1% achieved between 7 and 9, compared with 21.1% of A-A* grades last year.
Ofqual chief regulator Sally Collier said: ''Today's results reflect years of careful planning.
''We have used the same tried and tested principle of comparable outcomes, as in previous years, to ensure that this first cohort of students is not disadvantaged.
''If a student receives a grade 7 today, they could have expected to have received a grade A last year.
''And if they get a grade 4, they could have expected to get a grade C in 2016.''
Schools minister Nick Gibb said pupil and teachers are "rising to the challenge" of the new GCSEs.
Geoff Barton, general secretary of the Association of School and College Leaders, said: "Congratulations to the pupils and their teachers on this year's GCSE results which have been achieved in very challenging circumstances.
"They have performed miracles amidst a sea of curriculum change which continues unabated next year."
He added: "We are concerned to see a slight decline in the overall rate for grades C/ 4, and above, and fear that this may be the result of driving children down this narrow academic route which does not necessarily suit every child.
"In addition, the new reformed GCSEs are more challenging and children sit more exams."
There have been concerns that the new grading system is confusing, particularly to parents, universities and employers.
The DfE and Ofqual have said a wide range of resources and information has been produced to ensure everyone knows about the changes.
While the new grading system applies to England only, GCSEs in Wales and Northern Ireland are also undergoing reforms.
In Wales, new courses in English, Welsh and maths have been brought in this year, although pupils are still assessed throughout their studies, rather than only sitting exams at the end. New GCSEs in other subjects are being gradually introduced.
This year has also seen a large increase in English language entries in general, driven by many schools switching back to taking a GCSE instead of the equivalent international GCSE, which no longer counts in annual school league tables.
There is also an incentive for schools and colleges in England to enter pupils for both English GCSEs, as students' best result is then counted as double in the rankings.