A string of American triumphs in the pool and a near-flawless turn by U.S. women's gymnastics team on Tuesday night powered NBC to its strongest ratings of the 2016 Rio Summer Games, as some 33.4 million viewers tuned in for the network's primetime Olympics program.

According to Nielsen live-plus-same-day data, NBC's coverage of the fourth night of competition was its highest-rated thus far, averaging an 18.9 household rating from 8 p.m.-11:44 p.m. EDT. That marked a 13% decline from the 21.8 household rating NBC notched four years ago during the analogous evening in London, a delivery that would prove to be the high-water mark of the 2012 Olympics.

Through the first five nights in Rio, the NBC flagship network is averaging 27.9 million viewers and a 15.3 household rating, down 21% from 35.1 million viewers and a 19.4 rating.

While the broadcaster has yet to top its record-breaking performance of four years ago, it has managed to add to its total via its primetime cable coverage of more niche offerings (judo, weight lifting, table tennis, etc.) and live-streaming. According to NBC's research department, deliveries over NBCSN, Bravo and its various digital properties added some 2.7 million viewers to the broadcast network's Tuesday night totals, while plumping the overall household rating by 1.6 points.

Those ancillary deliveries could go a long way toward digging the Peacock out of a potentially ruinous make-goods scenario. In the absence of the cable and digital deliveries, NBC's 15.3 rating in prime represents a shortfall of between 15% and 20% from the ratings guarantees it made to advertisers in the run-up to the Olympics. (Buyers said the network promised to deliver ratings that matched or topped the 17.5 household rating it averaged over the course of the London Games; the highest estimate quoted to Ad Age was a 19.0.)

Roll up the cable and digital deliveries for the first four nights of competition, and NBC's average Olympics rating (including the opening ceremony) improves 9% to a 16.6, which obviously puts it within closer range of meeting its guarantees. But having started at a distinct disadvantage -- the opening ceremony was down 36% versus the London table-setter, a drop many trendspotters chalked up to an earlier-than-usual procession by Team USA (the Portuguese designation "Estados Unidos" pushed up the Yanks' appearance from 195th to 70th, thereby giving American viewers an excuse to tune out early) -- NBC remains in a tight spot. If it's going to soldier through the next 12 nights without having to hand over ADUs, or audience deficiency units, to unsatisfied advertisers, NBC will have to pull for an exceptional turnout on Thursday, Sunday and Tuesday nights, which are traditionally among the biggest draws. (The prospect of a last look at the incomparable dolphin-man hybrid Michael Phelps and a legendary performance by Simone Biles in the women's all-around gymnastics final couldn't possibly hurt.)

If a ratings rally isn't in the cards, NBC's first line of redress would be to offer makegoods within its remaining Olympics schedule, with top-tier clients getting first dibs at primetime inventory. In the worst-case scenario, the network runs out of reserved inventory before it can work out the ADUs, and clients would be offered a free pass in marquee properties such as "Sunday Night Football" and "The Voice."

As one might expect, some of the most dedicated in-game advertisers are official Olympics sponsors like Coca-Cola, McDonald's, Visa, Toyota and Samsung Mobile, although unaffiliated BMW and Chevrolet are presently the biggest spenders in NBC's primetime coverage. Automotive has accounted for nearly 20% of all Olympics TV spend; other leading categories include insurance, movie studios, financial services and quick-service restaurants.

All told, more than 300 brands have bought national ad time across NBC, NBCSN, Bravo, USA Network, CNBC and MSNBC. One highly visible client, Hillary Clinton's "Hillary for America" campaign, already has invested in 56 national spots, whereas the Donald J. Trump campaign hasn't spent a penny on Olympics inventory.

While 30-second primetime spots on NBC are commanding as much as $1.1 million a pop, the network has sacrificed a fair amount of paid-for inventory to promote its own wares. Of the three new scripted series NBC is bringing to the air this fall, the show that has far and away been the beneficiary of the heaviest Olympics promotional push is the drama "Timeless." Bowing Oct. 3 in the Monday 10 p.m. slot leading out of "The Voice," "Timeless" has been trotted out (in teaser form) no fewer than 100 times since the Olympic torch was lit last Friday night.