The London Olympics bronze medallist won 21-14, 21-17, in 40 minutes, at the Babu Banarasi Das Indoor stadium.
The two-time champion was tested by her younger opponent but held her nerve to eventually break a 15-month title drought after appearing in her 22nd final of her international career.
"It's an emotional moment for me. Loved the support I got. Lucknow has been my favourite city. I won my first title here in 2009. It feels good to win again. The win was more special as it came after such a long time," she said moments after her victory.
"Sindhu played very well. It was a great match and the crowd enjoyed it. She is great player, and also in top-10. I am happy that I pulled it off.
"I was little nervous, as I was playing in a final after a long time. But things went well for me," said Saina, who had last reached a final in the French Super Series in October, 2012.
Luck was on Saina's side, as a couple of controversial line calls helped the 23-year-old lead 3-0 initially and then extend it to 5-0.
Sindhu earned her first point when Saina hit wide, but the Commonwealth Games champion kept the pressure on her with some smashes to lead 8-2.
Sindhu slowly started, retrieving the shuttle and engaging in rallies, to narrow down the lead to 5-8. However, she was erratic at finishing the points and lagged 5-11 at the break.
After the breather, Sindhu scored with the help of her accurate over the head smashes and smart net play to narrow the deficit to 11-14. But she once again faltered with the length of her returns, allowing Saina to take a 19-13 lead.
After a long rally, an accurate smash and another point, it was advantage Saina after the first game.
Sindhu started the second game on an aggressive note and moved to 4-0. Saina soon started dictating terms and erased the deficit at 5-5.
While Saina used all her experience, Sindhu used her long arm and height to score and take an 8-6 lead.
But Saina used her deceptive shots and body line smashes build a healthy 12-9 lead. With Sindhu again hitting wide and long, Saina led 15-10. Sindhu won a long rally but better net play took Saina to 19-13.
At this stage, Sindhu gathered three points but a low flick return went to the net. That gave Saina four match-points.
A controversial line call helped Sindhu save one, but Saina caught her junior opponent at the net to complete the formalities without wasting any more time.
This is Saina's third straight victory over Sindhu. The two played at the inaugural Indian Badminton League (IBL) last year, where Saina got the better of the Sindhu on two occasions.
Saina has been battling poor form and injury issues for more than a year now, which saw her drop to world No 9 this week from No 2.
Sunday's victory helped her earn 7000 points and will also allow her to climb the ranking ladder.
Image: Saina Nehwal
Photograph: Michael Regan/Getty Images
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