The Nasdaq Composite has sold off sharply this year, tumbling into a bear market fueled by economic uncertainty. During that downturn, many excellent businesses saw their valuations crumble. For instance, shares of Nvidia (NVDA -2.85%) and MercadoLibre (MELI -0.13%) plunged 53% and 54%, respectively, marking their sharpest declines at any point in the past decade.

Losses like that can be scary, but investors need to step back and look at the big picture. Both businesses are still brimming with potential, and the ongoing sell-off represents a once-in-a-decade buying opportunity.

1. Nvidia: Graphics and accelerated computing

Chipmaker Nvidia reported disappointing results in the third quarter of fiscal 2023 (ended Oct. 30). Revenue dropped 17% to $5.9 billion, and earnings plunged 72% to $0.27 per diluted share. The impetus behind that dismal performance can be summed up as a challenging economic environment. High inflation blunted consumer spending on gaming chips, and the recent wave of COVID-19 lockdowns in China led to softness in demand for data center chips.

Worse yet, Nvidia provided guidance that fell short of Wall Street's consensus. The company expects revenue to fall 21% to $6 billion in the fourth quarter, driven by continued weakness in demand across its gaming, professional visualization, and data center segments. That said, the challenging economic environment is a temporary problem, meaning the long-term investment thesis has not changed.

Nvidia's graphics processing units (GPUs) are the gold standard in gaming, 3D design, and accelerated computing. In fact, the company holds over 90% market share in workstation graphics. Its GPUs power 71% of the fastest supercomputers on the planet, and its artificial intelligence (AI) platform has regularly set records in both training and inference at the MLPerf benchmarks, a series of objective tests designed to measure the performance for AI hardware and software.

Additionally, Nvidia reinforced its dominance in gaming and data center computing with subscription software. Its AI Enterprise suite helps businesses build and deploy AI applications that recognize images, understand speech, and make predictive recommendations. Those applications have use cases across virtually every industry, from manufacturing and logistics to retail and financial services. Likewise, Nvidia Omniverse software empowers creators to build metaverse applications like 3D worlds and intelligent avatars. Those technologies will only become more relevant in the future.

With that in mind, Nvidia puts its addressable market at $1 trillion, including $100 billion in gaming hardware, $150 billion in AI software, $150 billion in Omniverse software, $300 billion in data center hardware, and $300 billion in automotive solutions.

As a caveat, Nvidia may continue to struggle in the coming quarters, and that could drive the stock price even lower. But the company remains well positioned to capitalize on a massive market opportunity. And with shares trading at 13.8 times sales -- a discount to the three-year average of 20.3 times sales -- risk-tolerant investors should buy a few shares of this growth stock today.

2. MercadoLibre: E-commerce and digital payments

Latin American e-commerce giant MercadoLibre recently delivered a dazzling third-quarter report. Revenue climbed 45% to $2.7 billion -- representing 94% growth in its fintech business and 20% growth in its commerce business -- and GAAP earnings jumped 33% to $2.56 per diluted share. Those results are particularly impressive in light of suppressed consumer spending and unfavorable foreign exchange rates. Better yet, investors have good reason to believe that momentum will continue.

MercadoLibre operates the most visited online marketplace in Latin America, which itself is home to some of the fastest-growing e-commerce markets in the world. In fact, MercadoLibre will power almost 21% of online retail sales in Latin America this year, and its market share is expected to approach 22% next year, according to eMarketer. That success arises from its first-mover status and its ability to provide value-added services like logistics support and digital advertising tools.

MercadoLibre also operates a thriving fintech business. Mercado Credito provides merchant loans, consumer loans, and credit cards, and its credit portfolio climbed 146% in the third quarter. Similarly, Mercado Pago handles payment processing for merchants, both on and off the MercadoLibre marketplace, and it ranks as the third most popular digital wallet among Latin American consumers. Total payment volume increased 54% to $32.2 billion in the third quarter.

MercadoLibre is a key player in two large and growing markets. According to Statista, e-commerce spend across all relevant geographies will grow at 17% annually to reach $290 billion by 2027, while digital payment volume will grow at 15% annually to reach $510 billion by 2027.

Currently, shares trade at 4.6 times sales, an absolute bargain compared to the three-year average of 13.1 times sales. Investors should jump on that buying opportunity.