Sarfaraz hit an aggressive 74 from 78 balls before taking a wicket and four catches as Pakistan were bowled out for 222 in reply to India's 262 for seven.
Electing to bat first, India got off to a brisk start as Ankush Bains and Akhil Herwadkar put on 65 runs for the opening wicket, from 49 balls, before the former was bowled by pacer Irfanullah Shah.
Captain Vijay Zol departed cheaply after scoring just three, while Herwadkar and Ricky Bhui also fell in the space of few overs to leave India struggling at 94 for four in 20th over.
Sarfaraz and Sanju Samson, who played a solid innings of 68 from 101 balls, however, rescued India, putting on 119 runs for the fifth wicket that helped the team post a healthy score.
While Sarfaraz struck five fours and a six in his 78-ball knock, Samson found the fence twice and cleared it once during his 101-ball knock.
Both took their time to gauge the conditions and situation, but paced their innings differently. While Samson dropped anchor and held up one end, Sarfaraz looked for boundaries.
Sarfaraz swept the spinners and was successful in finding the gaps at regular intervals. After failing to score from the first 15 balls he faced, and surviving a dropped chance at slips, he opened up.
Samson too playing confidently at the other end. Both batsmen used their feet against the spinners to good effect and hit 36 runs in the Batting Powerplay to give the innings the much-needed impetus going into the final overs.
But Sarfaraz was out soon, falling to a mishit, and Samson too made his way back to the pavilion shortly after.
Deepak Hooda provided the late flourish, slamming a quick 22 from 18 balls.
Pakistan were off to a good start, as captain Sami Aslam and Imam-ul-Haq put on a 109-run opening stand from 142 balls. But the dismissal of Imam-ul-Haq, who was caught by Sarfaraz off Aamir Gani for 39, turned things around.
Sami was run-out for 64, courtesy some good work on the field by captain Zol, before Hooda ran through the middle order, claiming five wickets for 41 runs and also effecting a run-out.
This was India’s third victory in eight matches over Pakistan in the ICC Under-19 Cricket World Cup. Overall, India now leads 12-8 in 21 Under-19 matches to date.
In the other matches of the day, opener Shadman Islam became the first batsman of the 2014 tournament to hit a century as Bangladesh gave Afghanistan a cricket lesson when it won by 10 wickets at Abu Dhabi Oval 2; three-time former winner Australia thumped Namibia by 101 runs at Zayed Cricket Stadium, and Scotland made short work of Papua New Guinea (PNG) by six wickets at ICC Academy 1.
Shadman Islam slapped 14 fours and a six in an unconquered 126 that came off 142 deliveries, while Joyraz Sheik's 81 not out from 114 balls included 11 fours as Bangladesh achieved the 213 runs target with more than seven overs to spare.
Earlier, Mosaddek Hossain took three for 19 and Rahatul Ferdous bagged two for 38 as Afghanistan collected 212 with Mohammad Mujtaba top-scoring with 47.
Opener Matthew Short missed a century by four runs as Australia, winners in 1988, 2002 and 2010, had an easy sailing at the Zayed Cricket Stadium, where it overpowered Namibia by 101 runs.
Short hit nine fours in a 138-ball 96 and featured in an 80-run second wicket stand with Jaron Morgan (33), which was followed by a 100-run third wicket stand with Ben McDermott (45) as Australia scored 242 for seven after electing to bat first.
In turn, Namibia was bowled out for 141, as Matthew Fotia and James Bazley equally shared six wickets between them, conceding 23 and 25 runs respectively.
The only positive for Namibia from an otherwise disappointing day was an all-round performance by Bredell Wessells. With his medium-fast bowling, Wessells returned figures of four for 40 and then contributed 43 runs with the bat that included five fours and a six.
Short later said: "It's a bit disappointing not going all the way to a century, but the boys batted pretty well. One of the aims of today was to bat well throughout the middle overs and we had a few good partnerships through the middle."
Scores in brief:
Pool A: India beat Pakistan by 40 runs at Dubai International Cricket Stadium
India 262-7, 50 overs (Sarfaraz Khan 74, Sanju Samson 68, Akhil Herwadkar 41, Ankush Bains 24, Deepak Hooda 22 not out; Irfanullah Shah 2-32, Karamat Ali 2-37)
Pakistan 222 all out, 48.4 overs (Sami Aslam 64, Imam-ul-Haq 39, Saud Shakeel 32, Zia-ul-Haq 21; Deepak Hooda 5-41)
Man of the match – Sarfaraz Khan (India)
Pool A: Scotland beat Papua New Guinea (PNG) by six wickets at ICC Academy 1
PNG 108 all out, 36.3 overs (Ross McLean 3-15, Chayank Gosain 3-17, Mark Watt 2-23)
Scotland 110-4, 29.4 overs (Zander Muir 39 not out, Nick Farrar 26; Alei Nao 2-28, Kabua Morea 2-30)
Man of the match – Zander Muir (Scotland)
Pool B: Bangladesh beat Afghanistan by 10 wickets at Abu Dhabi Oval 2
Afghanistan 212 all out, 50 overs (Mohammad Mujtaba 47, Hashmatullah Shaidi 43, Nasir Ahmadzai 41; Mosaddek Hossain 3-19, Rahatul Ferdous 2-38)
Bangladesh 216-0, 42.3 overs (Shadman Islam 126 not out; Joyraz Sheik 81 not out)
Man of the match – Shadman Islam (Bangladesh)
Pool B: Australia beat Namibia by 101 runs at Zayed Cricket Stadium
Australia 242-7, 50 overs (Matthew Short 96, Ben McDermott 45, Jaron Morgan 33, Alex Gregory 25, Jake Doran 20; Bredell Wessells 4-50, JJ Smit 3-55)
Namibia 141 all out, 44.2 overs (Bredell Wessells 43, Jaen Kotze 23, Gerhard Erasmus 21, Matthew Fotia 3-23, James Bazley 3-25)
Man of the match – Matthew Short (Australia)
Image: Sarfaraz Khan
Photograph: 2014 © IDI/Getty Images
Mumbai cricket's wonderkids Sarfaraz, Musheer living father's dream
Record was not on mind, says Mumbai schoolboy Shaw after hitting 546
Bowling will determine India's Test future: Dravid
PHOTOS: India register 40-run victory over Pakistan in Under-19 World Cup
Kuldeep, Sarfaraz take India past Scotland in U-19 World Cup