How do you craft a cover letter that grabs attention right from the opening sentence in a competitive job market?

I'd agree with Emily on the hook. Too many cover letters I see ramble on about the applicant's home life. A good hook will definitely make them stand out. Also, cover letter writers need to stop thanking the reader for actually reading the letter! It's not just in the applicant's interest. Colleges and universities are reading letters to find interesting students, so reading letters is just as important as writing them - so you're on a level playing field of interest. 

Use your opening paragraph as a hook. This is where you convey genuine interest to create a connection between you and the company/ team/ person you’re addressing. For example: “I was excited to read about xyz in the news because…”, “I was inspired by your recent LinkedIn post around xyz because…” or “I’ve always admired x company’s mission to xyz because…” This thoughtful detail proves that you’ve done your homework. You don’t need to write a book here; in fact I’d argue that one sentence is stronger and feels real and convincing.