The 38-year-old Victoria Park Harriers runner took the top prize in a time of one hour, nine minutes and 36 seconds.
Martelletti set a new course record on his way to winning last year but was unable to better his time in the third Worthing Half Marathon.
Jeff Pyrah (1:10:22) and runner-up from 2017, Kevin Roja (1:10:29), were second and third respectively - unable to run Martelletti close.
The New Zealander, fresh from competiting in a cross-country event less than 24 hours earlier, was pleased to come out on top in cold and windy conditions.
He said: "I had it a bit harder today after competiting in a cross-country event yesterday. Some of the wind was pretty brutal, I was slowing down 30 seconds a mile but I kept pushing on and done it in a decent time.
"I was hoping to run a little quicker but I just hoped to get a solid run, I felt good and it was a strong finish.
"I won the Watford Half Marathon last week and I was probably about a minute quicker. There are a few hills to contend with in that one but it was nowhere as windy as it was today.
"I've been building up doing some cross-country ahead of the Rotterdam Marathon I'll be competing in later this year.
"Worthing is always on my radar, it's well organised so I'll be thinking about coming back to try and get a third win next year."
Cambridge runner George Schwiening was the first female to finish in a time of 1:19:46.
Brighton-based Arena 80 Athletics Club competitor Emily Proto (1:22:39) was the second women across the line, while Rebecca Bunting (1:24:04) completed the top-three female finishers.